CRITICAL DIFFERENCE

                          BY MURRAY LEINSTER

           [Transcriber's Note: This etext was produced from
                Astounding Science Fiction, July 1956. 
         Extensive research did not uncover any evidence that
         the U.S. copyright on this publication was renewed.]




                                   I


Massy waked that morning when the only partly-opened port of his
sleeping-cabin closed of itself and the room-warmer began to whir. He
found himself burrowed deep under his covering, and when he got his
head out of it the already-bright room was bitterly cold and his breath
made a fog about him.

He thought uneasily, _It's colder than yesterday!_ But a Colonial
Survey officer is not supposed to let himself seem disturbed, in
public, and the only way to follow that rule is to follow it in
private, too. So Massy composed his features, while gloom filled him.
When one has just received senior service rating and is on one's very
first independent survey of a new colonial installation, the unexpected
can be appalling. The unexpected was definitely here, on Lani III.

He'd been a Survey Candidate on Khali II and Taret and Arepo I,
all of which were tropical, and a Junior Officer on Menes III and
Thotmes--one a semiarid planet and the other temperate-volcanic--and
he'd done an assistant job on Saril's solitary world, which was
nine-tenths water. But this first independent survey on his own was
another matter. Everything was wholly unfamiliar. An ice planet with a
minus point one habitability rating was upsetting in its peculiarities.
He knew what the books said about glacial-world conditions, but that
was all.

The denseness of the fog his breath made seemed to grow less as the
room-warmer whirred and whirred. When by the thinness of the mist he
guessed the temperature to be not much under freezing, he climbed out
of his bunk and went to the port to look out. His cabin, of course,
was in one of the drone-hulls that had brought the colony's equipment
to Lani III. The other emptied hulls were precisely ranged in order
outside. They were duly connected by tubular galleries, and very
painstakingly leveled. They gave an impression of impassioned tidiness
among the upheaved, ice-coated mountains all about.

He gazed down the long valley in which the colony lay. There were
monstrous slanting peaks on either side. They partly framed the morning
sun. Their sides were ice. The flanks of every mountain in view were
ice. The sky was pale. The sun had four sun-dogs placed geometrically
about it. It shone coldly upon this far-out world. Normal post-midnight
temperatures in this valley ranged around ten below zero--and this
was technically summer. But it was colder than ten below zero now. At
noon there were normally tiny trickling rills of surface-thaw running
down the sunlit sides of the mountains--but they froze again at night
and the frost replaced itself after sunset. And this was a sheltered
valley--warmer than most of the planet's surface. The sun had its
sun-dogs every day, on rising. There were nights when the brighter
planets had star-pups, too.

       *       *       *       *       *

The phone-plate lighted and dimmed and lighted and dimmed. They
did themselves well on Lani III--but the parent world was in this
same solar system. That was rare. Massy stood before the plate and
it cleared. Herndon's face peered unhappily out of it. He was even
younger than Massy, and inclined to lean heavily on the supposedly vast
experience of a Senior Officer of the Colonial Survey.

"Well?" said Massy--and suddenly felt very undignified in his
sleeping-garments.

"We're picking up a beam from home," said Herndon anxiously, "but we
can't make it out."

Because the third planet of the sun Lani was being colonized from
the second, inhabited world, communication with the colony's base
was possible. A tight beam could span a distance which was only
light-minutes across at conjunction, and not much over a light-hour
at opposition--as now. But the beam communication had been broken
for the past few weeks, and shouldn't be possible again for some
weeks more. The sun lay between. One couldn't expect normal
sound-and-picture transmission until the parent planet had moved past
the scrambler-fields of Lani. But something had come through. It would
be reasonable for it to be pretty well hashed when it arrived.

"They aren't sending words or pictures," said Herndon uneasily. "The
beam is wabbly and we don't know what to make of it. It's a signal, all
right, and on the regular frequency. But there are all sorts of stray
noises, and still in the midst of it there's some sort of signal we
can't make out. It's like a whine, only it stutters. It's a broken-up
sound of one pitch."

Massy rubbed his chin reflectively. He remembered a course in
information theory just before he'd graduated from the Service Academy.
Signals made by pulses, and pitch-changes and frequency-variations.
Information was what couldn't be predicted without information. And he
remembered with gratitude a seminar on the history of communication,
just before he'd gone out on his first field job as a Survey Candidate.

"Hm-m-m," he said with a trace of self-consciousness. "Those
noises--the stuttering ones. Would they be, on the whole, of no more
than two different durations? Like--hm-m-m--_Bzz bzz bzzzzzz bzz_?"

He felt that he lost dignity by making such ribald sounds. But
Herndon's face brightened.

"That's it!" he said relievedly. "That's it! Only they're high-pitched
like--" His voice went falsetto. "_Bzz bzz bzz bzzzzz bzz bzz!_"

It occurred to Massy that they sounded like two idiots. He said with
dignity:

"Record everything you get, and I'll try to decode it." He added:
"Before there was voice communication there were signals by light
and sounds in groups of long and short units. They came in groups,
to stand for letters, and things were spelled out. Of course there
were larger groups which were words. Very crude system, but it worked
when there was great interference, as in the early days. If there's
some emergency, your home world might try to get through the sun's
scrambler-field that way."

"Undoubtedly!" said Herndon, with even greater relief. "No question,
that's it!"

He regarded Massy with great respect as he clicked off. His image
faded. The plate was clear.

       *       *       *       *       *

_He thinks I'm wonderful_, thought Massy wryly. _Because I'm Colonial
Survey. But all I know is what's been taught me. It's bound to show up
sooner or later. Damn!_

He dressed. From time to time he looked out the port again. The
intolerable cold of Lani III had intensified, lately. There was some
idea that sunspots were somehow the cause. He couldn't make out
sunspots with the naked eye, but the sun did look pale, with its
accompanying sun-dogs. Massy was annoyed by them. They were the result
of microscopic ice-crystals suspended in the air. There was no dust on
this planet, but there was plenty of ice! It was in the air and on the
ground and even under it. To be sure, the drills for the foundation
of the great landing-grid had brought up cores of frozen humus along
with frozen clay, so there must have been a time when this world had
known clouds and seas and vegetation. But it was millions, maybe
hundreds of millions of years ago. Right now, though, it was only warm
enough to have an atmosphere and very slight and partial thawings in
direct sunlight, in sheltered spots, at midday. It couldn't support
life, because life is always dependent on other life, and there is a
temperature below which a natural ecological system can't maintain
itself. The past few weeks, the climate had been such that even
human-supplied life looked dubious.

Massy slipped on his Colonial Survey uniform with its palm-tree
insignia. Nothing could be much more inappropriate than palm-tree
symbols on a planet with sixty feet of permafrost. Massy reflected
wryly, _The construction gang calls it a blast, instead of a tree,
because we blow up when they try to dodge specifications. But
specifications have to be met! You can't bet the lives of a colony or
even a ship's crew on half-built facilities!_

He marched down the corridor from his sleeping room, with the dignity
he painstakingly tried to maintain for the sake of the Colonial Survey.
It was a pretty lonely business, being dignified all the time. If
Herndon didn't look so respectful, it would have been pleasant to be
more friendly. But Herndon revered him. Even his sister Riki--

But Massy put her firmly out of his mind. He was on Lani III to check
and approve the colony installations. There was the giant landing-grid
for spaceships, which took power from the ionosphere to bring heavily
loaded space-vessels gently to the ground, and in between times took
power from the same source to supply the colony's needs. It also
lifted visiting spacecraft the necessary five planetary diameters out
when they took off again. There was power-storage in the remote event
of disaster to that giant device. There was a food-reserve and the
necessary resources for its indefinite stretching in case of need. That
usually meant hydroponic installations. There was a reason for the
colony, which would make it self-supporting--here a mine. All these
things had had to be finished and operable and inspected by a duly
qualified Colonial Survey officer before the colony could be licensed
for unlimited use. It was all very normal and official, but Massy was
the newest Senior Survey Officer on the list, and this was the first of
his independent operations. He felt inadequate, sometimes.

He passed through the vestibule between this drone-hull and the next.
He went directly to Herndon's office. Herndon, like himself, was newly
endowed with authority. He was actually a mining-and-minerals man and
a youthful prodigy in that field, but when the director of the colony
was taken ill while a supply ship was aground, he went back to the home
planet and command devolved on Herndon. _I wonder_, thought Massy, _if
he feels as shaky as I do?_

       *       *       *       *       *

When he entered the office, Herndon sat listening to a literal hash
of noises coming out of a speaker on his desk. The cryptic signal had
been relayed to him, and a recorder stored it as it came. There were
cracklings and squeals and moaning sounds, and sputters and rumbles
and growls. But behind the façade of confusion there was a tiny,
interrupted, high-pitched noise. It was a monotone whining not to be
confused with the random sounds accompanying it. Sometimes it faded
almost to inaudibility, and sometimes it was sharp and clear. But it
was a distinctive sound in itself, and it was made up of short whines
and longer ones of two durations only.

"I've put Riki at making a transcription of what we've got," said
Herndon with relief as he saw Massy. "She'll make short marks for the
short sounds, and long ones for the long. I've told her to try to
separate the groups. We've got a full half hour of it, already."

Massy made an inspired guess.

"I would expect it to be the same message repeated over and over," he
said. He added. "And I think it would be decoded by guessing at the
letters in two-letter and three-letter words, as clues to longer ones.
That's quicker than statistical analysis of frequency."

Herndon instantly pressed buttons under his phone-plate. He relayed the
information to Riki, his sister, as if it were gospel. Massy remembered
guiltily that it wasn't gospel. It was simply a trick recalled from
his boyhood, when he was passionately interested in secret languages.
His interest had faded when he realized he had no secrets to record or
transmit.

Herndon turned from the phone-plate.

"Riki says she's already learned to recognize some groups," he
reported, "but thanks for the advice. Now what?"

Massy sat down. He'd have liked some coffee, but he was being treated
with such respect that the role of demigod was almost forced on him.

"It seems to me," he observed, "that the increased cold out here might
not be local. Sunspots--"

Herndon jittered visibly. He silently handed over a sheet of paper
with observation-figures on top and a graph below them which related
the observations to each other. They were the daily, at-first-routine,
measurements of the solar constant from Lani III. The graph-line almost
ran off the paper at the bottom.

"To look at this," he admitted, "you'd think the sun was going out. Of
course it can't be," he added hastily. "Not possibly! But there is an
extraordinary number of sunspots. Maybe they'll clear. But meanwhile
the amount of heat reaching us is dropping. As far as I know there's
no parallel to it. Night temperatures are thirty degrees lower than
they should be. Not only here, either, but at all the robot weather
stations that have been spotted around the planet. They average forty
below zero minimum, instead of ten. And--there is that terrific lot of
sunspots...."

He looked hopefully at Massy. Massy frowned. Sunspots are things
about which nothing can be done. Yet the habitability of a borderline
planet, anyhow, can very well depend on them. An infinitesimal change
in sun heat can make a serious change in any planet's temperature. In
the books, the ancient mother planet Earth was said to have entered
glacial periods through a drop of only three degrees in the planet-wide
temperature, and to have been tropic almost to its poles from a rise of
only six. It had been guessed that glacial periods in the planet where
humanity began had been caused by coincidences of sunspot maxima.

This planet was already glacial to its equator. There was a genuinely
abnormal number of sunspots on Lani, its sun. Sunspots could account
for worsening conditions here, perhaps. _That message from the inner
planet could be bad_, thought Massy, _if the solar constant drops and
stays down a while._ But aloud he said:

"There couldn't be a really significant permanent change. Not quickly,
anyhow. Lani's a Sol-type star, and they aren't variables, though of
course any dynamic system like a sun will have cyclic modifications of
one sort or another. But they usually cancel out."

He sounded encouraging, even to himself. But there was a stirring
behind him. Riki Herndon had come silently into her brother's office.
She looked pale. She put papers down on her brother's desk.

"But," she said evenly, "while cycles sometimes cancel, sometimes they
enhance each other. They heterodyne. That's what's happening."

       *       *       *       *       *

Massy scrambled to his feet, flushing. Herndon said sharply:

"What? Where'd you get that stuff, Riki?"

She nodded at the sheaf of papers she'd just laid down.

"That's the news from home." She nodded again, to Massy. "You were
right. It was the same message, repeated over and over. And I decoded
it like children decode each other's secret messages. I did that to Ken
once. He was twelve, and I decoded his diary, and I remember how angry
he was that I'd found out he didn't have any secrets."

She tried to smile. But Herndon wasn't listening. He read swiftly.
Massy saw that the under sheets were rows of dots and dashes,
painstakingly transcribed and then decoded. There were letters under
each group of marks.

Herndon was very white when he'd finished. He handed the sheet to
Massy. Riki's handwriting was precise and clear. Massy read:

"FOR YOUR INFORMATION THE SOLAR CONSTANT IS DROPPING RAPIDLY DUE TO
COINCIDENCE OF CYCLIC VARIATIONS IN SUNSPOT ACTIVITY WITH PREVIOUS
UNOBSERVED LONG CYCLES APPARENTLY INCREASING THE EFFECT MAXIMUM
IS NOT YET REACHED AND IT IS EXPECTED THAT THIS PLANET WILL BECOME
UNINHABITABLE FOR A TIME ALREADY KILLING FROSTS HAVE DESTROYED CROPS
IN SUMMER HEMISPHERE IT IS IMPROBABLE THAT MORE THAN A SMALL PART OF
THE POPULATION CAN BE SHELTERED AND WARMED THROUGH DEVELOPING GLACIAL
CONDITIONS WHICH WILL REACH TO EQUATOR IN TWO HUNDRED DAYS THE COLD
CONDITIONS ARE COMPUTED TO LAST TWO THOUSAND DAYS BEFORE NORMAL SOLAR
CONSTANT RECURS THIS INFORMATION IS SENT YOU TO ADVISE IMMEDIATE
DEVELOPMENT OF HYDROPONIC FOOD SUPPLY AND OTHER PRECAUTIONS MESSAGE
ENDS FOR YOUR INFORMATION THE SOLAR CONSTANT IS DROPPING RAPIDLY DUE TO
COINCIDENCE OF CYCLIC--"

Massy looked up. Herndon's face was ghastly. Massy said in some
grimness:

"Kent IV's the nearest world your planet could hope to get help from.
A mail liner will make it in two months. Kent IV might be able to send
three ships--to get here in two months more. That's no good!"

He felt sick. Human-inhabited planets are far apart. The average
distance of stars of all types--there is on an average between four
and five light-years of distance between suns. They are two months'
spaceship journey apart. And not all stars are sol-type or have
inhabited planets. Colonized worlds are like isolated islands in an
unimaginably vast ocean, and the ships that ply between them at thirty
light-speeds seem merely to creep. In ancient days on the mother planet
Earth, men sailed for months between ports, in their clumsy sailing
ships. There was no way to send messages faster than they could travel.
Nowadays there was little improvement. News of the Lani disaster
could not be transmitted. It had to be carried, as between stars, and
carriage was slow and response to news of disaster was no faster.

The inner planet, Lani II, had twenty millions of inhabitants, as
against the three hundred people in the colony on Lani III. The outer
planet was already frozen, but there would be glaciation on the inner
world in two hundred days. Glaciation and human life are mutually
exclusive. Human beings can survive only so long as food and power hold
out, and shelter against really bitter cold cannot be improvised for
twenty million people! And, of course, there could be no outside help
on any adequate scale. News of the need for it would travel too slowly.
One other world might hear in two months, and send what aid it could
in four. But the next would not hear for four months, and could not
send help in less than eight. It would take five Earth-years to get a
thousand ships to Lani II--and a thousand ships could not rescue more
than one per cent of the population. But in five years there would not
be nearly so many people left alive.

       *       *       *       *       *

Herndon licked his lips. There were three hundred people in the
already-frozen colony. They had food and power and shelter. They had
been considered splendidly daring to risk the conditions here. But
all their home world would presently be like this. And there was no
possibility of equipping everybody there as the colonists were equipped.

"Our people," said Riki in a thin voice, "all of them.... Mother and
father and--the others. Our cousins. All our friends. Home is going to
be like ... like that!"

She jerked her head toward a port which let in the frigid
colony-world's white daylight. Her face worked.

Massy was aware of an extreme unhappiness on her account. For himself,
of course, the tragedy was less. He had no family. He had very few
friends. But he could see something that had not occurred to them as
yet.

"Of course," he said, "it's not only their trouble. If the solar
constant is really dropping like that ... why things out here will be
pretty bad too. A lot worse than they are now. We'll have to get to
work to save ourselves!"

Riki did not look at him. Herndon bit his lips. It was plain that their
own fate did not concern them immediately. But when one's home world
is doomed, one's personal safety seems a very trivial matter.

There was silence save for the crackling, tumultuous noises that came
out of the speaker on Herndon's desk. In the midst of that confused
sound there was a wavering, whining, high-pitched note which swelled
and faded and grew distinct again.

"We," said Massy without confidence, "are right now in the conditions
they'll face a good long time from now."

Herndon said dully:

"But we couldn't live here without supplies from home. Or even without
the equipment we brought. But they can't get supplies from anywhere,
and they can't make such equipment for everybody! They'll die!" He
swallowed, and there was a clicking noise in his throat. "They ... they
know it, too. So they ... warn us to try to save ourselves because ...
they can't help us any more."

There are many reasons why a man can feel shame that he belongs to a
race which can do the things that some men do. But sometimes there are
reasons to be proud, as well. The home world of this colony was doomed,
but it sent a warning to the tiny group on the colony-world, to allow
them to try to save themselves.

"I ... wish we were there to ... share what they have to face," said
Riki. Her voice sounded as if her throat hurt. "I ... don't want to
keep on living if ... everybody who ... ever cared about us is going to
die!"

Massy felt lonely. He could understand that nobody would want to live
as the only human alive. Nobody would want to live as a member of the
only group of people left alive. And everybody thinks of his home
planet as all the world there is. _I don't think that way_, thought
Massy. _But maybe it's the way I'd feel about living if Riki were to
die._ It would be natural to want to share any danger or any disaster
she faced. Which he was.

"L-look!" he said, stammering a little "You don't see! It isn't a case
of your living while they die! If your home world becomes like this,
what will this be like? We're farther from the sun! We're colder to
start with! Do you think we'll live through anything they can't take?
Food supplies or no, equipment or no, do you think we've got a chance?
Use your brains!"

Herndon and Riki stared at him. And then some of the strained look left
Riki's face and body. Herndon blinked, and said slowly:

"Why ... that's so! We were thought to be taking a terrific risk when
we came here. But it'll be as much worse here--Of course! We are in the
same fix they're in!"

He straightened a little. Color actually came back into his face. Riki
managed to smile. And then Herndon said almost naturally:

"That makes things look more sensible! We've got to fight for our
lives, too! And we've very little chance of saving them! What do we do
about it, Massy?"




                                  II


The sun was halfway toward mid-sky, and still attended by its sun-dogs,
though they were fainter than at the horizon. The sky was darker. The
mountain peaks reached skyward, serene and utterly aloof from the
affairs of men. This was a frozen world, where there should be no
inhabitants. The city was a fleet of metal hulks, neatly arranged on
the valley floor, emptied of the material they had brought for the
building of the colony. At the upper end of the valley the landing-grid
stood. It was a gigantic skeleton of steel, rising from legs of
unequal length bedded in the hillsides, and reaching two thousand feet
toward the stars. Human figures, muffled almost past recognition,
moved about a catwalk three-quarters of the way up. There was a tiny
glittering below where they moved. They were, of course, men using
sonic ice-breakers to shatter the frost which formed on the framework
at night. Falling shards of crystal made a liquidlike flashing. The
landing-grid needed to be cleared every ten days or so. Left uncleared,
it would acquire an increasingly thick coating of ice. In time it could
collapse. But long before that time it would have ceased to operate,
and without its operation there could be no space travel. Rockets for
lifting spaceships were impossibly heavy, for practical use. But the
landing-grids could lift them out to the unstressed space where Lawlor
drives could work, and draw them to ground with cargoes they couldn't
possibly have carried if they'd needed rockets.

Massy reached the base of the grid on foot. It was not far from the
village of drone-hulls. He was dwarfed by the ground-level upright
beams. He went through the cold-lock to the small control-house at the
grid's base.

He nodded to the man on standby as he got painfully out of his muffling
garments.

"Everything all right?" he asked.

The standby operator shrugged. Massy was Colonial Survey. It was his
function to find fault, to expose inadequacies in the construction and
operation of colony facilities. _It's natural for me to be disliked by
men whose work I inspect_, thought Massy. _If I approve it doesn't mean
anything, and if I protest, it's bad._ He had always been lonely, but
it was a part of the job.

"I think," he said painstakingly, "that there ought to be a change in
maximum no-drain voltage. I'd like to check it."

The operator shrugged again. He pressed buttons under a phone-plate.

"Shift to reserve power," he commanded, when a face appeared in the
plate. "Gotta check no-drain juice."

"What for?" demanded the face in the plate.

"You-know-who's got ideas," said the grid operator scornfully. "Maybe
we've been skimping something. Maybe there's some new specification we
didn't know about. Maybe anything! But shift to reserve power."

The face in the screen grumbled. Massy swallowed. It was not a Survey
officer's privilege to maintain discipline. But there was no particular
virtue in discipline here and now. He watched the current-demand dial.
It stood a little above normal day-drain, which was understandable. The
outside temperature was down. There was more power needed to keep the
dwellings warm, and there was always a lot of power needed in the mine
the colony had been formed to exploit. The mine had to be warmed for
the men who worked to develop it.

The demand-needle dropped abruptly, and hung steady, and dropped again
and again as additional parts of the colony's power-uses were switched
to reserve. The needle hit bottom. It stayed there.

Massy had to walk around the standby man to get at the voltmeter. It
was built around standard, old-fashioned vacuum tubes--standard for
generations, now. Massy patiently hooked it up and warmed the tubes
and tested it. He pushed in the contact-plugs. He read the no-drain
voltage. He licked his lips and made a note. He reversed the leads, so
it would read backward. He took another reading. He drew in his breath
very quietly.

"Now I want the power turned on in sections," he told the operator.
"The mine first, maybe. It doesn't matter. But I want to get
voltage-readings at different power take-offs."

The operator looked pained. He spoke with unnecessary elaboration to
the face in the phone-plate, and grudgingly went through with the
process by which Massy measured the successive drops in voltage with
power drawn from the ionosphere. The current available from a layer of
ionized gas is, in effect, the current-flow through a conductor with
marked resistance. It is possible to infer a gas' ionization from the
current it yields.

       *       *       *       *       *

The cold-lock door opened. Riki Herndon came in, panting a little.

"There's another message from home," she said sharply. Her voice
seemed strained. "They picked up our answering-beam and are giving the
information you asked for."

"I'll be along," said Massy. "I just got some information here."

He got into his cold-garments again. He followed her out of the
control-hut.

"The figures from home aren't good," said Riki evenly, when mountains
visibly rose on every hand around them. "Ken says they're much worse
than he thought. The rate of decline in the solar constant's worse than
we figured or could believe."

"I see," said Massy, inadequately.

"It's absurd!" said Riki fiercely. "It's monstrous! There've been
sunspots and sunspot cycles all along! I learned about them in school!
I learned myself about a four-year and a seven-year cycle, and that
there were others! They should have known! They should have calculated
in advance! Now they talk about sixty-year cycles coming in with a
hundred-and-thirty-year cycle to pile up with all the others--But
what's the use of scientists if they don't do their work right and
twenty million people die because of it?"

Massy did not consider himself a scientist, but he winced. Riki raged
as they moved over the slippery ice. Her breath was an intermittent
cloud about her shoulders. There was white frost on the front of her
cold-garments.

He held out his hand quickly as she slipped, once.

"But they'll beat it!" said Riki in a sort of angry pride. "They're
starting to build more landing-grids, back home. Hundreds of them!
Not for ships to land by, but to draw power from the ionosphere! They
figure that one ship-size grid can keep nearly three square miles of
ground warm enough to live on! They'll roof over the streets of cities.
Then they'll plant food-crops in the streets and gardens, and do what
hydroponic growing they can. They are afraid they can't do it fast
enough to save everybody, but they'll try!"

Massy clenched his hands inside their bulky mittens.

"Well?" demanded Riki. "Won't that do the trick?"

Massy said: "No."

"Why not?" she demanded.

"I just took readings on the grid, here. The voltage and the
conductivity of the layer we draw power from, both depend on
ionization. When the intensity of sunlight drops, the voltage drops and
the conductivity drops, too. It's harder for less power to flow to the
area the grid can tap--and the voltage-pressure is lower to drive it."

"Don't say any more!" cried Riki. "Not another word!"

Massy was silent. They went down the last small slope. They passed the
opening of the mine--the great drift which bored straight into the
mountain. They could look into it. They saw the twin rows of brilliant
roof-lights going toward the heart of the stony monster.

They had almost reached the village when Riki said in a stifled voice:

"How bad is it?"

"Very," admitted Massy. "We have here the conditions the home planet
will have in two hundred days. Originally we could draw less than a
fifth the power they count on from a grid on Lani II."

Riki ground her teeth.

"Go on!" she said challengingly.

"Ionization here is down ten per cent," said Massy. "That means the
voltage is down--somewhat more. A great deal more. And the resistance
of the layer is greater. Very much greater. When they need power most,
on the home planet, they won't draw more from a grid than we do now. It
won't be enough."

They reached the village. There were steps to the cold-lock of
Herndon's office-hull. They were ice-free, because like the village
walkways they were warmed to keep frost from depositing on them. Massy
made a mental note.

In the cold-lock, the warm air pouring in was almost stifling. Riki
said defiantly:

"You might as well tell me now!"

"We could draw one-fifth as much power, here, as the same sized grid
would yield on your home world," he said grimly. "We are drawing--call
it sixty per cent of normal. A shade over one-tenth of what they must
expect to draw when the real cold hits them. But their estimates are
nine times too high." He said heavily, "One grid won't warm three
square miles of city. About a third of one is closer. But--"

"That won't be the worst!" said Riki in a choked voice. "Is that right?
How much good will a grid do?"

Massy did not answer.

The inner cold-lock door opened. Herndon sat at his desk, even paler
than before, listening to the hash of noises that came out of the
speaker. He tapped on the desktop, quite unconscious of the action. He
looked almost desperately at Massy.

"Did she ... tell you?" he asked in a numb voice. "They hope to save
maybe half the population. All the children anyhow--"

"They won't," said Riki bitterly.

"Better go transcribe the new stuff that's come in," said her brother
dully. "We might as well know what it says."

Riki went out of the office. Massy laboriously shed his cold-garments.
He said uncomfortably:

"The rest of the colony doesn't know what's up yet. The operator at the
grid didn't, certainly. But they have to know."

"We'll post the messages on the bulletin board," said Herndon
apathetically. "I wish I could keep it from them. It's not fun to live
with. I ... might as well not tell them just yet."

"To the contrary," insisted Massy. "They've got to know right away!
You're going to issue orders and they'll need to understand how urgent
they are!"

Herndon looked absolutely hopeless.

"What's the good of doing anything?" When Massy frowned, he added as
if exhausted: "Seriously, is there any use? You're all right. A Survey
ship's due to take you away. It's not coming because they know there's
something wrong, but because your job should be finished about now.
But it can't do any good! It would be insane for it to land at home.
It couldn't carry away more than a few dozen refugees, and there are
twenty million people who're going to die. It might offer to take some
of us. But ... I don't think many of us would go. I wouldn't. I don't
think Riki would."

"I don't see--"

"What we've got right here," said Herndon, "is what they're going
to have back home. And worse. But there's no chance for us to keep
alive here! You are the one who pointed it out! I've been figuring,
and the way the solar-constant curve is going--I plotted it from the
figures they gave us--it couldn't possibly level out until the oxygen,
anyhow, is frozen out of the atmosphere here. We aren't equipped to
stand anything like that, and we can't get equipped. There couldn't
be equipment to let us stand it indefinitely! Anyhow the maximum cold
conditions will last two thousand days back home--six Earth-years.
And there'll be storage of cold in frozen oceans and piled-up
glaciers--It'll be twenty years before home will be back to normal
in temperature, and the same here. Is there any point in trying to
live--just barely to survive--for twenty years before there'll be a
habitable planet to go back to?"

Massy said irritably:

"Don't be a fool! Doesn't it occur to you that this planet is a perfect
experiment-station, two hundred days ahead of the home world, where
ways to beat the whole business can be tried? If we can beat it here,
they can beat it there!"

Herndon said detachedly:

"Can you name one thing to try here?"

"Yes," snapped Massy. "I want the walk-heaters and the step-heaters
outside turned off. They use power to keep walkways clear of frost and
doorsteps not slippery. I want to save that heat!"

Herndon said without interest:

"And when you've saved it, what will you do with it?"

"Put it underground to be used as needed!" Massy said angrily. "Store
it in the mine! I want to put every heating-device we can contrive
to work in the mine! To heat the rock! I want to draw every watt the
grid will yield and warm up the inside of the mountain while we can
draw power to do it with! I want the deepest part of the mine too hot
to enter! We'll lose a lot of heat, of course. It's not like storing
electric power! But we can store heat now, and the more we store the
more will be left when we need it!"

       *       *       *       *       *

Herndon thought heavily. Presently he stirred slightly.

"Do you know, that is an idea--" He looked up. "Back home there was a
shale-oil deposit up near the icecaps. It wasn't economical to mine it.
So they put heaters down in bore-holes and heated up the whole shale
deposit! Drill-holes let out the hot oil vapors to be condensed. They
got out every bit of oil without disturbing the shale! And then ...
why ... the shale stayed warm for years. Farmers bulldozed soil over
it and raised crops with glaciers all around them! That could be done
again. They could be storing up heat back home!"

Then he drooped.

"But they can't spare power to warm up the ground under cities. They
need all the power they've got to build roofs. And it takes time to
build grids."

Massy snapped:

"Yes, if they're building regulation ones! By the time they were
finished they'd be useless! The ionization here is dropping already.
But they don't need to build grids that will be useless later! They
can weave cables together on the ground and hang them in the air by
helicopters! They wouldn't hold up a landing ship for an instant, but
they'll draw power right away! They'll even power the helis that hold
them up! Of course they've defects! They'll have to come down in high
winds. They won't be dependable. But they can put heat in the ground
to come out under roofs, to grow food by, to save lives by. What's the
matter with them?"

Herndon stirred again. His eyes ceased to be dull and lifeless.

"I'll give the orders for turning off the sidewalks. And I'll send what
you just said back home. They ... should like it."

He looked very respectfully at Massy.

"I guess you know what I'm thinking right now," he said awkwardly.

Massy flushed. It was not dignified for a Colonial Survey officer to
show off. He felt that Herndon was unduly impressed. But Herndon didn't
see that the device wouldn't solve anything. It would merely postpone
the effects of a disaster. It could not possibly prevent them.

"It ought to be done," he said curtly. "There'll be other things to be
done, too."

"When you tell them to me," said Herndon warmly, "they'll get done!
I'll have Riki put this into that pulse-code you explained to us and
she'll get it off right away!"

He stood up.

"I didn't explain the code to her!" insisted Massy. "She was already
translating it when you gave her my suggestion!"

"All right," said Herndon. "I'll get this sent back at once!"

He hurried out of the office. _This_, thought Massy irritably, _is how
reputations are made, I suppose. I'm getting one._ But his own reaction
was extremely inappropriate. If the people of Lani II did suspend
helicopter-supported grids of wire in the atmosphere, they could warm
masses of underground rock and stone and earth. They could establish
what were practically reservoirs of life-giving heat under their
cities. They could contrive that the warmth from below would rise only
as it was needed. But--

       *       *       *       *       *

Two hundred days to conditions corresponding to the colony-planet.
Then two thousand days of minimum-heat conditions. Then very, very
slow return to normal temperature, long after the sun was back to its
previous brilliance. They couldn't store enough heat for so long. It
couldn't be done. It was ironic that in the freezing of ice and the
making of glaciers the planet itself could store cold.

And there would be monstrous storms and blizzards on Lani II as it
cooled. As cold conditions got worse the wire grids could be held aloft
for shorter and shorter periods, and each time they would pull down
less power than before. Their effectiveness would diminish even faster
than the need for effectiveness increased.

Massy felt even deeper depression as he worked out the facts. His
proposal was essentially futile. It would be encouraging, and to a
very slight degree and for a certain short time it would palliate the
situation on the inner planet. But in the long run its effect would be
zero.

He was embarrassed, too, that Herndon was so admiring. Herndon would
tell Riki that he was marvelous. She might--though cagily--be inclined
to agree. But he wasn't marvelous. This trick of a flier-supported
grid was not new. It had been used on Saril to supply power for giant
peristaltic pumps emptying a polder that had been formed inside a ring
of indifferently upraised islands.

_All I know_, thought Massy bitterly, _is what somebody's showed me
or I've read in books. And nobody's showed or written how to handle a
thing like this!_

He went to Herndon's desk. Herndon had made a new graph on the
solar-constant observations forwarded from home. It was a strictly
typical curve of the results of coinciding cyclic changes. It was
the curve of a series of frequencies at the moment when they were all
precisely in phase. From this much one could extrapolate and compute--

Massy took a pencil, frowning unhappily. His fingers clumsily formed
equations and solved them. The result was just about as bad as it
could be. The change in brightness of the sun Lani would not be enough
to be observed on Kent IV--the nearest other inhabited world--when
the light reached there four years from now. Lani would never be
classed as a variable star, because the total change in light and heat
would be relatively minute. But the formula for computing planetary
temperatures is not simple. Among its factors are squares and cubes of
the variables. Worse, the heat radiated from a sun's photosphere varies
not as the square or cube, but as the fourth power of its absolute
temperature. A very small change in the sun's effective temperature,
producible by sunspots, could make an altogether disproportionate
difference in the warmth its worlds received.

Massy's computations were not pure theory. The data came from Sol
itself, where alone in the galaxy there had been daily solar-constant
measurements for three hundred years. The rest of his deductions were
based ultimately on Earth observations, too. Most scientific data had
to refer back to Earth to get an adequate continuity. But there was no
possible doubt about the sunspot data, because Sol and Lani were of the
same type and nearly equal size.

Using the figures on the present situation, Massy reluctantly arrived
at the fact that here, on this already-frozen world, the temperature
would drop until CO_{2}, froze out of the atmosphere. When that
happened, the temperature would plummet until there was no really
significant difference between it and that of empty space. It is carbon
dioxide which is responsible for the greenhouse effect, by which a
planet is in thermal equilibrium only at a temperature above its
surroundings--as a greenhouse in sunlight is warmer than the outside
air.

The greenhouse effect would vanish soon on the colony-world. When it
vanished on the mother planet--

Massy found himself thinking, _If Riki won't leave when the Survey ship
comes, I'll resign from the Service. I'll have to if I'm to stay. And I
won't go unless she does._




                                  III


"If you want to come, it's all right," said Massy ungraciously.

He waited while Riki slipped into the bulky cold-garments that were
needed out-of-doors in the daytime, and were doubly necessary at night.
There were heavy boots with inches-thick insulating soles, made in
one piece with the many-layered trousers. There was the air-puffed,
insulated over-tunic with its hood and mittens which were a part of
the sleeves.

"Nobody goes outside at night," she said when they stood together in
the cold-lock.

"I do," he told her. "I want to find out something."

The outer door opened and he stepped out. He held his arm for her,
because the steps and walkway were no longer heated. Now they were
covered with a filmy layer of something which was not frost, but a
faint, faint bloom of powder. It was the equivalent of dust, but it was
microscopic snow-crystals frozen out of the air by the unbearable chill
of night.

There was no moon, of course, yet the ice-clad mountains glowed
faintly. The drone-hulls arranged in such an orderly fashion were dark
against the frosted ground. There was silence: stillness: the feeling
of ancient quietude. No wind stirred anywhere. Nothing moved. Nothing
lived. The soundlessness was enough to crack the eardrums.

Massy threw back his head and gazed at the sky for a very long time.
Nothing. He looked down at Riki.

"Look at the sky," he commanded.

She raised her eyes. She had been watching him. But as she gazed
upward she almost cried out. The sky was filled with stars in
innumerable variety. But the brighter ones were as stars had never
been seen before. Just as the sun in daylight had been accompanied
by its sun-dogs--pale phantoms of itself ranged about it--so the
brighter distant suns now shone from the center of rings of their own
images. They no longer had the look of random placing. Those which
were most distinct were patterns in themselves, and one's eyes strove
instinctively to grasp the greater pattern in which such seeming
artifacts must belong.

"Oh ... beautiful!" cried Riki softly, yet almost afraid.

"Look!" he insisted. "Keep looking!"

She continued to gaze, moving her eyes about hopefully. It was such a
sight as no one could have imagined. Every tint and every color; every
possible degree of brightness appeared. And there were groups of stars
of the same brilliance which almost made triangles, but not quite.
There were rose-tinted stars which almost formed an arc, but did not.
And there were arrays which were almost lines and nearly formed squares
and polygons, but never actually achieved them.

"It's ... beautiful!" said Riki breathlessly. "But what must I look
for?"

"Look for what isn't there," he ordered.

       *       *       *       *       *

She looked, and the stars were unwinking, but that was not
extraordinary. They filled all the firmament, without the least space
in which some tiny sparkle of light was not to be found. But that was
not remarkable, either. Then there was a vague flickering grayish glow
somewhere indefinite. It vanished. Then she realized.

"There's no aurora!" she exclaimed.

"That's it," said Massy. "There've always been auroras here. But
no longer. We may be responsible. I wish I thought it wise to turn
everything back to reserve power for a while. We could find out. But we
can't afford it. There was just the faintest possible gray flickering
just now. But there ought to be armies of light marching across the
sky. The aurora here--it was never missing! But it's gone now."

"I ... looked at it when we first landed," admitted Riki. "It was
unbelievable! But it was terribly cold, out of shelter. And it happened
every night, so I said to myself I'd look tomorrow, and then tomorrow
again. So it got so I never looked at all."

Massy kept his eyes where the faint gray flickering had been. And
once one realized, it was astonishing that the former nightly play of
ghostly colors should be absent.

"The aurora," he said dourly, "happens in the very upper limits of the
air ... fifty ... seventy ... ninety miles up, when God-knows-what
emitted particles from the sun come streaking in, drawn by the
planet's magnetic field. The aurora's a phenomenon of ions. We tap the
ionosphere a long way down from where it plays, but I'm wondering if we
stopped it."

"We?" said Riki, shocked. "We--humans?"

"We tap the ions of their charges," he said somberly, "that the
sunlight made by day. We're pulling in all the power we can. I wonder
if we've drained the aurora of its energy, too."

Riki was silent. Massy gazed, still searching. But he shook his head.

"It could be," he said in a carefully detached voice. "We didn't draw
much power by comparison with the amount that came. But the ionization
is an ultraviolet effect. Atmospheric gases don't ionize too easily.
After all, if the solar constant dropped a very little, it might mean a
terrific drop in the ultraviolet part of the spectrum--and that's what
makes ions of oxygen and nitrogen and hydrogen and such. The ion-drop
could easily be fifty times as great as the drop in the solar constant.
And we're drawing power from the little that's left."

Riki stood very still. The cold was horrible. Had there been a wind, it
could not have been endured for an instant. But the air was motionless.
Yet its coldness was so great that the inside of one's nostrils ached,
and the inside of one's chest was aware of chill. Even through the
cold-garments there was the feeling as of ice without.

"I'm beginning," said Massy, "to suspect that I'm a fool. Or maybe I'm
an optimist. It might be the same thing. I could have guessed that
the power we could draw would drop faster than our need for power
increased. If we've drained the aurora of its light, we're scraping
the bottom of the barrel. And it's a shallower barrel than one would
suspect."

There was stillness again. Riki stood mousy-quiet. _When she realizes
what this means_, thought Massy grimly, _she won't admire me so much.
Her brother's built me up. But I've been a fool, figuring out excuses
to hope. She'll see it._

"I think," said Riki quietly, "that you're telling me that after all we
can't store up heat to live on, down in the mine."

"We can't," agreed Massy grimly. "Not much, nor long. Not enough to
matter."

"So we won't live as long as Ken expects?"

"Not nearly as long," said Massy evenly. "He's hoping we can find out
things to be useful back on Lani II. But we'll lose the power we can
get from our grid long before even their new grids are useless. We'll
have to start using our reserve power a lot sooner. It'll be gone--and
us with it--before they're really in straits for living-heat."

Riki's teeth began to chatter.

"This sounds like I'm scared," she said angrily, "but I'm not! I'm just
freezing! If you want to know, I'd a lot rather have it the way you
say! I won't have to grieve over anybody, and they'll be too busy to
grieve for me! Let's go inside while it's still warm!"

He helped her back into the cold-lock, and the outer door closed. She
was shivering uncontrollably when the warmth came pouring in.

They went into Herndon's office. He came in as Riki was peeling off the
top part of her cold-garments. She still shivered. He glanced at her
and said to Massy:

"There's been a call from the grid-control shack. It looks like there's
something wrong, but they can't find anything. The grid is set for
maximum power-collection, but it's bringing in only fifty thousand
kilowatts!"

"We're on our way back to savagery," said Massy, with an attempt at
irony.

It was true. A man can produce two hundred and fifty watts from his
muscles for a reasonable length of time. When he has no more power, he
is a savage. When he gains a kilowatt of energy from the muscles of a
horse, he is a barbarian--but the new power cannot be directed wholly
as he wills. When he can apply it to a plow he has high barbarian
culture, and when he adds still more he begins to be civilized. Steam
power put as much as four kilowatts to work for every human being in
the first industrialized countries, and in the mid-twentieth century
there was sixty kilowatts per person in the more advanced nations.
Nowadays, of course, a modern culture assumed five hundred as a
minimum. But there was less than half that in the colony on Lani II.
And its environment made its own demands.

"There can't be any more," said Riki, trying to control her shivering.
"We're even using the aurora and there isn't any more power. It's
running out. We'll go even before the people at home, Ken."

Herndon's features looked very pinched.

"But we can't! We mustn't!" He turned to Massy. "We do them good, back
home! There was panic. Our report about cable-grids has put heart in
people. They're setting to work--magnificently! So we're some use! They
know we're worse off than they are, and as long as we hold on they'll
be encouraged! We've got to keep going somehow!"

Riki breathed deeply until her shivering stopped. Then she said calmly:

"Haven't you noticed, Ken, that Mr. Massy has the viewpoint of his
profession? His business is finding things wrong with things. He was
deposited in our midst to detect defects in what we did and do. He has
the habit of looking for the worst. But I think he can turn the habit
to good use. He did turn up the idea of cable-grids."

"Which," said Massy, "turns out to be no good at all. They'd be some
good if they weren't needed, really. But the conditions that make them
necessary make them useless!"

Riki shook her head.

"They are useful!" she said firmly. "They're keeping people at home
from despairing. Now, though, you've got to think of something else.
If you think of enough things, one will do good the way you want--more
than making people feel better."

"What does it matter how people feel?" he demanded bitterly. "What
difference do feelings make? Facts are facts! One can't change facts!"

Riki said with no less firmness:

"We humans are the only creatures in the universe who don't do anything
else! Every other creature accepts facts. It lives where it is born,
and it feeds on the food that is there for it, and it dies when the
facts of nature require it to. We humans don't. Especially we women!
We won't let men do it, either! When we don't like facts--mostly about
ourselves--we change them. But important facts we disapprove of--we ask
men to change for us. And they do!"

She faced Massy. Rather incredibly, she grinned at him.

"Will you please change the facts that look so annoying just now,
please? Please?" Then she elaborately pantomimed an over-feminine
girl's look of wide-eyed admiration. "You're so big and strong! I just
know you can do it--for me!"

She abruptly dropped the pretense and moved toward the door. She
half-turned then, and said detachedly:

"But about half of that is true."

       *       *       *       *       *

The door slid shut behind her. Massy thought bitterly, _Her brother
admires me. She probably thinks I really can do something!_ It suddenly
occurred to him that she knew a Colonial Survey ship was due to stop
by here to pick him up. She believed he expected to be rescued, even
though the rest of the colony could not be, and most of it wouldn't
consent to leave their kindred when the death of mankind in this solar
system took place. He said awkwardly:

"Fifty thousand kilowatts isn't enough to land a ship."

Herndon frowned. Then he said:

"Oh. You mean the Survey ship that's to pick you up can't land? But it
can go in orbit and put down a rocket landing-boat for you."

Massy flushed.

"I wasn't thinking of that. I'd something more in mind. I ... rather
like your sister. She's ... pretty wonderful. And there are some other
women here in the colony, too. About a dozen all told. As a matter of
self-respect I think we ought to get them away on the Survey ship. I
agree that they wouldn't consent to go. But if they had no choice--if
we could get them on board the grounded ship, and they suddenly found
themselves ... well ... kidnaped and outward-bound not by their own
fault.... They could be faced with the accomplished fact that they had
to go on living."

Herndon said evenly:

"That's been in the back of my mind for some time. Yes. I'm for that.
But if the Survey ship can't land--"

"I believe I can land it regardless," said Massy doggedly. "I can find
out, anyhow. I'll need to try things. I'll need help ... work done.
But I want your promise that if I can get the ship to ground you'll
conspire with her skipper and arrange for them to go on living."

Herndon looked at him.

"Some new stuff--in a way," said Massy uncomfortably. "I'll have to
stay aground to work it. It's also part of the bargain that I shall.
And, of course, your sister can't know about it, or she can't be fooled
into living."

Herndon's expression changed a little.

"What'll you do? Of course it's a bargain."

"I'll need some metals we haven't smelted so far," said Massy.
"Potassium if I can get it, sodium if I can't, and at worst I'll settle
for zinc. Cesium would be best, but we've found no traces of it."

Herndon said thoughtfully:

"No-o-o. I think I can get you sodium and potassium, from rocks. I'm
afraid no zinc. How much?"

"Grams," said Massy. "Trivial quantities. And I'll need a miniature
landing-grid built. Very miniature."

Herndon shrugged his shoulders.

"It's over my head. But just to have work to do will be good for
everybody. We've been feeling more frustrated than any other humans in
history. I'll go round up the men who'll do the work. You talk to them."

       *       *       *       *       *

The door closed behind him. Massy very deliberately got out of his
cold-clothing. He thought, _She'll rave when she finds her brother and
I have deceived her._ Then he thought of the other women. _If any of
them are married, we'll have to see if there's room for their husbands.
I'll have to dress up the idea. Make it look like reason for hope, or
the women would find out. But not many can go_--

He knew very closely how many extra passengers could be carried on a
Survey ship, even in such an emergency as this. Living quarters were
not luxurious, at best. Everything was cramped and skimped. Survey
ships were rugged, tiny vessels which performed their duties amid
tedium and discomfort and peril for all on board. But they could carry
away a very few unwilling refugees to Kent IV.

He settled down at Herndon's desk to work out the thing to be done.

It was not unreasonable. Tapping the ionosphere for power was something
like pumping water out of a pipe-well in sand. If the water-table
was high, there was pressure to force the water to the pipe, and one
could pump fast. If the water-table were low, water couldn't flow
fast enough. The pump would suck dry. In the ionosphere, the level
of ionization was at once like the pressure and the size of the
sand-grains. When the level was high, the flow was vast because the
sand-grains were large and the conductivity high. But as the level
lessened, so did the size of the sand-grains. There was less to draw,
and more resistance to its flow.

But there had been one tiny flicker of auroral light over by the
horizon. There was still power aloft. If Massy could in a fashion prime
the pump: if he could increase the conductivity by increasing the ions
present around the place where their charges were drawn away--why--he
could increase the total flow. It would be like digging a brick-well
where a pipe-well had been. A brick-well draws water from all around
its circumference.

So Massy computed carefully. It was ironic that he had to go to such
trouble simply because he didn't have test-rockets like the Survey uses
to get a picture of a planet's weather-pattern. They rise vertically
for fifty miles or so, trailing a thread of sodium-vapor behind them.
The trail is detectable for some time, and ground-instruments record
each displacement by winds blowing in different directions at different
speeds, one over the other. Such a rocket with its loading slightly
changed would do all Massy had in mind. But he didn't have one, so
something much more elaborate was called for.

_She'll think I'm clever_, he reflected wryly, _but all I'm doing
is what I've been taught. I wouldn't have to work it out if I had a
rocket._

Still, there was some satisfaction in working out this job. A
landing-grid has to be not less than half a mile across and two
thousand feet high because its field has to reach out five planetary
diameters to handle ships that land and take off. To handle solid
objects it has to be accurate--though power can be drawn with an
improvisation. To thrust a sodium-vapor bomb anywhere from twenty to
fifty miles high--why--he'd need a grid only six feet wide and five
high. It could throw much higher, of course. It could hold, at that.
But doubling the size would make accuracy easier.

He tripled the dimensions. There would be a grid eighteen feet across
and fifteen high. Tuned to the casing of a small bomb, it could hold it
steady at seven hundred and fifty thousand feet--far beyond necessity.
He began to make the detail drawings.

       *       *       *       *       *

Herndon came back with half a dozen chosen colonists. They were young
men, technicians rather than scientists. Some of them were several
years younger than Massy. There were grim and stunned expressions on
some faces, but one tried to pretend nonchalance, and two seemed trying
to suppress fury at the monstrous occurrence that would destroy not
only their own lives, but everything they remembered on the planet
which was their home. They looked almost challengingly at Massy.

He explained. He was going to put a cloud of metallic vapor up in the
ionosphere. Sodium if he had to, potassium if he could, zinc if he
must. Those metals were readily ionized by sunlight--much more readily
than atmospheric gases. In effect, he was going to supply a certain
area of the ionosphere with material to increase the efficiency of
sunshine in providing electric power. As a sideline, there would be
increased conductivity from the normal ionosphere.

"Something like this was done centuries ago, back on Earth," he
explained carefully. "They used rockets, and made sodium-vapor clouds
as much as twenty and thirty miles long. Even nowadays the Survey uses
test-rockets with trails of sodium-vapor. It will work to some degree.
We'll find out how much."

He felt Herndon's eyes upon him. They were almost dazedly respectful.
But one of the technicians said coldly:

"How long will those clouds last?"

"That high, three or four days," Massy told him. "They won't help much
at night, but they should step up power-intake while the sun shines on
them."

A man in the back said crisply:

"Hup!" The significance was, "Let's go!" Then somebody said feverishly,
"What do we do? Got working drawings? Who makes the bombs? Who does
what? Let's get at this!"

Then there was confusion, and Herndon had vanished. Massy suspected
he'd gone to have Riki put this theory into dot-and-dash code for
beam-transmission back to Lani II. But there was no time to stop him.
These men wanted precise information, and it was half an hour before
the last of them had gone out with free-hand sketches, and had come
back for further explanation of a doubtful point, and other men had
come in hungrily to demand a share in the job.

When he was alone again, Massy thought, _Maybe it's worth doing because
it'll get Riki on the Survey ship. But they think it means saving the
people back home!_

Which it didn't. Taking energy out of sunlight is taking energy out
of sunlight, no matter how you do it. Take it out as electric power,
and there's less heat left. Warm one place with electric power, and
everywhere else is a little colder. There's an equation. On this
colony-world it wouldn't matter, but on the home world it would. The
more there was trickery to gather heat, the more heat was needed. Again
it might postpone the death of twenty million people, but it would
never, never, never prevent it.

       *       *       *       *       *

The door slid aside and Riki came in. She stammered a little.

"I ... just coded what Ken told me to send back home. It will ... it
will do everything! It's wonderful! I ... wanted to tell you!"

Massy writhed internally. It wasn't wonderful.

"Consider," he said in a desperate attempt to take it lightly,
"consider that I've taken a bow."

He tried to smile. It was not a success. And Riki suddenly drew a deep
breath and looked at him in a new fashion.

"Ken's right," she said softly. "He says you can't get conceited.
You're not satisfied with yourself even now, are you?" She smiled,
rather gravely. Then she said, "But what I like is that you aren't
really smart. A woman can make you do things. I have!"

He looked at her uneasily. She grinned.

"I, even I, can at least pretend to myself that I help bring this
about! If I hadn't said please change the facts that are so annoying,
and if I hadn't said you were big and strong and clever--I'm going to
tell myself for the rest of my life that I helped make you do it!"

Massy swallowed.

"I'm afraid," he said miserably, "that it won't work again."

She cocked her head on one side.

"No?"

He stared at her apprehensively. And then with a bewildering change of
emotional reaction, he saw that her eyes were filled with tears. She
stamped her foot.

"You're ... horrible!" she cried. "Here I come in, and ... and if
you think you can get me kidnaped to safety ... without even telling
me that you 'rather like' me, like you told my brother, or that 'I'm
pretty wonderful'--If you think."

He was stunned, that she knew. She stamped her foot again.

"For Heaven's sake!" she wailed. "Do I have to _ask_ you to kiss me?"




                                  IV


During the last night of preparation, Massy sat by a thermometer
registering the outside temperature. He hovered over it as one might
over a sick child. He watched it and sweated, though the inside
temperature of the drone-hull was lowered to save power. There was
nothing he could actually do. At midnight the thermometer said it
was seventy degrees below zero Fahrenheit. At halfway to dawn it was
eighty degrees below zero Fahrenheit. The hour before dawn it was
eighty-five degrees below zero. Then he sweated profusely. The meaning
of the slowed descent was that carbon dioxide was being frozen out of
the upper layers of the atmosphere. The frozen particles were drifting
slowly downward, and as they reached lower and faintly warmer levels
they returned to the state of gas. But there was a level, above the
CO_{2}, where the temperature was plummeting.

The height to which carbon dioxide existed was dropping--slowly, but
inexorably. And above the carbon-dioxide level there was no bottom
limit to the temperature. The greenhouse effect was due to CO_{2}.
Where it wasn't, the cold of space moved down. If at ground-level the
thermometer read ever so slightly lower than one hundred and nine below
zero--why--everything was finished. Without the greenhouse effect, the
night-side of the planet would lose its remaining heat with a rush.
Even the day-side, once cold enough, would lose heat to emptiness as
fast as it came from the sun. Minus one hundred and nine point three
was the critical reading. If it went down to that, it would plunge to a
hundred and fifty--two hundred degrees below zero! And it would never
come up again.

There would be rain at nightfall--a rain of oxygen frozen to a
liquid and splashing on the ground. Human life would be quite simply
impossible, in any shelter and under any conditions. Even spacesuits
would not protect against an atmosphere sucking heat from it at that
rate. A spacesuit can be heated against the loss of temperature due to
radiation in a vacuum. It could not be heated against nitrogen which
would chill it irresistibly by contact.

But, as Massy sweated over it, the thermometer steadied at minus
eighty-five degrees. When the dawn came, it rose to seventy. By
mid-morning, the temperature in bright sunshine was no lower than
sixty-five degrees below zero.

But there was no bounce left in Massy when Herndon came for him.

"Your phone-plate's been flashing," said Herndon, "and you didn't
answer. Must have had your back to it. Riki's over in the mine,
watching them get things ready. She was worried that she couldn't call
you. Asked me to find out what was the trouble."

Massy said heavily:

"Has she got something to heat the air she breathes?"

"Naturally," said Herndon. He added curiously, "What's the matter?"

"We almost took our licking," Massy told him. "I'm afraid for tonight,
and tomorrow night, too. If the CO_{2} freezes--"

"We'll have power!" Herndon insisted. "We'll build ice tunnels and ice
domes. We'll build a city under ice, if we have to. But we'll have
power. We'll be all right!"

"I doubt it very much," said Massy. "I wish you hadn't told Riki of the
bargain to get her away from here when the Survey ship comes!"

Herndon grinned.

"Is the little grid ready?" asked Massy.

"Everything's set," said Herndon exuberantly. "It's in the mine-tunnel
with radiant heaters playing on it. The bombs are ready. We made enough
to last for months, while we were at it. No use taking chances!"

Massy looked at him queerly. Then he said:

"We might as well go out and try the thing, then."

       *       *       *       *       *

But he was very tired. He was not elated. _Riki can't be gotten away_,
he thought wearily, _and I'm not going to go because it isn't quite
fitting to go and leave her. They'll all be rejoicing presently, but
nothing's settled._ Then he thought with exquisite irony, _She thinks
I was inspired to genius by her, when I haven't done a thing I wasn't
taught or didn't get out of books!_

He put on the cold-garments as they were now modified for the
increased frigidity. Nobody could breathe air at minus sixty-five
degrees without getting his lungs frost-bitten. So there was now a
plastic mask to cover one's face, and the air one breathed outdoors was
heated as it came through a wire-gauze snout. But still it was not wise
to stay out of shelter for too long a time.

Massy went out-of-doors. He stepped out of the cold-lock and gazed
about him. The sun seemed markedly paler, and now it had lost its
sun-dogs again. Ice crystals no longer floated in the almost congealed
air. The sky was dark. It was almost purple, and it seemed to Massy
that he could detect faint flecks of light in it. They would be stars,
shining in the daytime.

There seemed to be no one about at all, only the white coldness of the
mountains. But there was a movement at the mine-drift, and something
came out of it. Four men appeared, muffled up like Massy himself. They
rolled the eighteen-foot grid out of the mine-mouth, moving it on those
inflated bags which are so much better than rollers for rough terrain.
They looked absurdly like bears with steaming noses, in their masks and
clothing. They had some sort of powered pusher with them, and they got
the metal cage to the very top of a singularly rounded stone upcrop
which rose in the center of the valley.

"We picked that spot," said Herndon's muffled voice through the chill,
"because by shifting the grid's position it can be aimed, and be on a
solid base. Right?"

"Quite all right," said Massy. "We'll go work it."

He moved heavily across the valley, in which nothing moved except
the padded figures of the four technicians. Their wire-gauze
breathing-masks seemed to emit smoke. They waved to him in greeting.

_I'm popular again_, he thought drearily, _but it doesn't matter.
Getting the Survey ship to ground won't help now, since Riki's
forewarned. And this trick won't solve anything permanently on the home
planet. It'll just postpone things._

He had a very peculiar ache inside. A Survey officer is naturally
lonely. Massy had been lonely before he even entered the Service. He
hadn't had a feeling of belonging anywhere, or with anyone, and no
planet was really his home. Now he could believe that he belonged
with someone. But there was the slight matter of a drop in the solar
constant of an unimportant sol-type sun, and nothing could come of it.

Even when Riki--muffled like the rest--waved to him from the mouth of
the tunnel, his spirits did not lift. The thing he wanted was to look
forward to years and years of being with Riki. He wanted, in fact, to
look forward to forever. And there might not be a tomorrow.

"I had the control board rolled out here," she called breathlessly
through her mask. "It's cold, but you can watch!"

It wouldn't be much to watch. If everything went all right, some
dial-needles would kick over violently, and their readings would go up
and up. But they wouldn't be readings of temperature. Presently the
big grid would report increased power from the sky. But tonight the
temperature would drop a little farther. Tomorrow night it would drop
farther still. When it reached one hundred and nine point three degrees
below zero at ground-level--why it would keep on falling indefinitely.
Then it wouldn't matter how much power could be drawn from the sky. The
colony would die.

       *       *       *       *       *

One of the figures that looked like a bear now went out of the
mine-mouth, trudging toward the grid. It carried a muffled,
well-wrapped object in its arms. It stooped and crept between the
spokes of the grid. It put the object on the stone. Massy traced cables
with his eyes. From the grid to the control board. From the board back
to the reserve-power storage cells, deep in the mountain.

"The grid's tuned to the bomb," said Riki breathlessly, close beside
him. "I checked that myself!"

The bearlike figure out in the valley jerked at the bomb. There was a
small rising cloud of grayish vapor. It continued. The figure climbed
hastily out of the grid. When the man was clear, Massy threw a switch.

There was a very tiny whining sound, and the wrapped, ridiculously
smoking object leaped upward. It seemed to fall toward the sky. There
was no more of drama than that. An object the size of a basketball
fell upward, swiftly, until it disappeared. That was all.

Massy sat quite still, watching the control-board dials. Presently he
corrected this, and shifted that. He did not want the bomb to have too
high an upward velocity. At a hundred thousand feet it would find very
little air to stop the rise of the vapor it was to release.

The field-focus dial reached its indication of one hundred thousand
feet. Massy reversed the lift-switch. He counted and then switched the
power off. The small, thin whine ended.

He threw the power-intake switch, which could have been on all the
time. The power-yield needle stirred. The minute grid was drawing
power like its vaster counterpart. But its field was infinitesimal by
comparison. It drew power as a soda straw might draw water from wet
sand.

Then the intake-needle kicked. It swung sharply, and wavered, and then
began a steady, even, climbing movement across the markings on the
dial-face. Riki was not watching that.

"They see something!" she panted. "Look at them!"

The four men who had trundled the smaller grid to its place, now stared
upward. They flung out their arms. One of them jumped up and down. They
leaped. They practically danced.

"Let's go see," said Massy.

He went out of the tunnel with Riki. They gazed upward. And directly
overhead, where the sky was darkest blue and where it had seemed that
stars shone through the daylight--there was a cloud. It seemed to
Massy, very quaintly, that it was no bigger than a man's hand. But it
grew. Its edges were yellow--saffron-yellow. It expanded and spread.
Presently it began to thin. As it thinned, it began to shine. It was
luminous. And the luminosity had a strange, familiar quality.

Somebody came panting down the tunnel, from inside the mountain.

"The grid--" he panted. "The big grid! It's ... pumping power! Big
power! BIG power!"

He went pounding back, to gaze raptuously at the new position of a thin
black needle on a large white dial, and to make incoherent noises of
rejoicing as it moved very, very slowly toward higher and ever higher
readings.

But Massy looked puzzledly at the sky, as if he did not quite believe
his eyes. The cloud now expanded very slowly, but still it grew. And it
was not regular in shape. The bomb had not shattered quite evenly, and
the vapor had poured out more on one side than the other. There was a
narrow, arching arm of brightness--

"It looks," said Riki breathlessly, "like a comet!"

And then Massy froze in every muscle. He stared at the cloud he had
made aloft, and his hands clenched in their mittens, and he swallowed
convulsively behind his cold-mask.

"Th-that's it," he said in a very queer voice indeed. "It's ... very
much like a comet. I'm glad you said that! We can make something even
more like a comet. We ... we can use all the bombs we've made, right
away, to make it. And we've got to hurry so it won't get any colder
tonight!"

Which, of course, sounded like insanity. Riki looked apprehensively at
him. But Massy had just thought of something. And nobody had taught it
to him and he hadn't gotten it out of books. But he'd seen a comet.

The new idea was so promising that he regarded it with anguished unease
for fear it would not hold up. It was an idea that really ought to
change the facts resulting naturally from a lowered solar constant in a
sol-type star.

       *       *       *       *       *

Half the colony set to work to make more bombs when the effect of the
second bomb showed up. They were not very efficient, at first, because
they tended to want to stop work and dance, from time to time. But they
worked with an impassioned enthusiasm. They made more bomb-casings, and
they prepared more sodium and potassium metal and more fuses, and more
insulation to wrap around the bombs to protect them from the cold of
airless space.

Because these were to go out to airlessness. The miniature grid could
lift and hold a bomb steady in its field-focus at seven hundred and
fifty thousand feet. But if a bomb was accelerated all the way out to
that point, and the field was then snapped off--Why, it wasn't held
anywhere. It kept on going with its attained velocity. And it burst
when its fuse decided that it should, whereupon immediately a mass of
sodium and potassium vapor, mixed with the fumes of high explosive,
flung itself madly in all directions, out between the stars. Absolute
vacuum tore the compressed gasified metals apart. The separate atoms,
white-hot from the explosion, went swirling through sunlit space. The
sunlight was dimmed a trifle, to be sure. But individual atoms of the
lighter alkaline-earth metals have marked photo-electric properties. In
sunshine these gas-molecules ionized, and therefore spread more widely,
and did not coalesce into even microscopic droplets.

They formed, in fact, a cloud in space. An ionized cloud, in which no
particle was too large to be responsive to the pressure of light. The
cloud acted like the gases of a comet's tail. It was a comet's tail,
though there was no comet. And it was an extraordinary comet's tail
because it is said that you can put a comet's tail in your hat, at
normal atmospheric pressure. But this could not have been put in a hat.
Even before it turned to gas, it was the size of a basketball. And, in
space, it glowed.

It glowed with the brightness of the sunshine on it, which was light
that would normally have gone away through the interstellar dark. And
it filled one corner of the sky. Within one hour it was a comet's tail
ten thousand miles long, which visibly brightened the daytime heavens.
And it was only the first of such reflecting clouds.

The next bomb set for space exploded in a different quarter, because
Massy'd had the miniature grid wrestled around the upcrop to point in a
new and somewhat more carefully chosen line. The third bomb spattered
brilliance in a different section still. And the brilliance lasted.

Massy flung his first bombs recklessly, because there could be more.
But he was desperately anxious to hang as many comet tails as possible
around the colony-planet before nightfall. He didn't want it to get any
colder.

And it didn't. In fact, there wasn't exactly any real nightfall on Lani
III that night.

The planet turned on its axis, to be sure. But around it, quite close
by, there hung gigantic streamers of shining gas. At their beginning,
those streamers bore a certain resemblance to the furry wild-animal
tails that little boys like to have hanging down from hunting-caps.
Only they shone. And as they developed they merged, so that there
was an enormous shining curtain about Lani III. There were draperies
of metal-mist to capture sunlight that should have been wasted, and
to diffuse very much of it to Lani II. At midnight there was only
one spot in all the night-sky where there was really darkness. That
was directly overhead--directly outward from the planet from the
sun. Gigantic shining streamers formed a wall, a tube, of comet-tail
material, yet many times more dense and therefore brighter--which
shielded the colony-world against the dark and cold, and threw upon it
a brilliant, warming brightness.

       *       *       *       *       *

Riki maintained stoutly that she could feel the warmth from the sky,
but that was improbable. But certainly heat did come from somewhere.
The thermometer did not fall at all, that night. It rose. It was up to
fifty below zero at dawn. During the day--they sent out twenty more
bombs that second day--it was up to twenty degrees below zero. By the
day after, there was highly competent computation from the home planet,
and the concrete results of abstruse speculation, and the third day's
bombs were placed with optimum spacing for heating purposes.

And by dawn of the fourth day the air was a balmy five degrees below
zero, and the day after that there was a small running stream in the
valley at midday.

There was talk of stocking the stream with fish, on the morning the
Survey ship came in. The great landing-grid gave out a deep-toned,
vibrant, humming note, like the deepest possible note of the biggest
organ that could be imagined. A speck appeared very, very high up in a
pale-blue sky with trimmings of golden gas-clouds. The Survey ship came
down and down and settled as a shining silver object in the very center
of the gigantic red-painted landing-grid.

Later, her skipper came to find Massy. He was in Herndon's office. The
skipper struggled to keep sheer blankness out of his expression.

"What ... what the hell?" he demanded querulously of Massy. "This
is the damnest sight in the whole galaxy, and they tell me you're
responsible! There've been ringed planets before, and there've been
comets and who-knows what! But shining gas pipes aimed at the sun, half
a million miles across.... What the? There are two of them! Both the
occupied planets!"

Herndon explained with a bland succinctness why the curtains hung in
space. There was a drop in the solar constant--

The skipper exploded. He wanted facts! Details! Something to report!
And dammit, he wanted to know!

Massy was automatically on the defensive when the skipper shot his
questions to him. A Senior Colonial Survey officer is not revered by
the Survey ship-service officers. Men like Massy can be a nuisance to a
hard-working ship's officer. They have to be carried to unlikely places
for their work of checking over colonial installations. They have to be
put down on hard-to-get-at colonies, and they have to be called for,
sometimes, at times and places which are inconvenient. So a man in
Massy's position is likely to feel unpopular.

"I'd just finished the survey here," he said defensively, "when a cycle
of sunspot cycles matured. All the sunspot periods got in phase, and
the solar constant dropped. So I naturally offered what help I could to
meet the situation."

The skipper regarded him incredulously.

"But ... it couldn't be done!" he said blankly. "They told me how
you did it, but ... it couldn't be done! Do you realize that these
vapor-curtains will make fifty borderline worlds fit for use? Half a
pound of sodium-vapor a week!" He gestured helplessly. "They tell me
the amount of heat reaching the surface here has been upped by fifteen
per cent! D'you realize what _that_ means?"

"I haven't been worrying about it," admitted Massy. "There was a local
situation and something had to be done. I ... er ... remembered things,
and Riki suggested something I mightn't have thought of, and it's
worked out like this." Then he said abruptly: "I'm not leaving. I'll
get you to take my resignation back. I ... I think I'm going to settle
here. It'll be a long time before we get really temperate-climate
conditions here, but we can warm up a valley like this for
cultivation, and ... well ... it's going to be a rather satisfying
job. It's a brand-new planet with a brand-new ecological system to be
established----"

The skipper of the Survey ship sat down hard. Then the sliding door of
Herndon's office opened and Riki came in. The skipper stood up again.
Massy rather awkwardly made the introduction. Riki smiled.

"I'm telling him," said Massy, "that I'm resigning from the Service to
settle down here."

Riki nodded. She put her hand in proprietary fashion on Massy's arm.
The Survey skipper cleared his throat.

"I'm not going to take it," he said doggedly. "There've got to be
detailed reports on how this business works. Dammit, if vapor-clouds in
space can be used to keep a planet warm, they can be used to shade a
planet, too! If you resign, somebody else will have to come out here to
make observations and work out the details of the trick! Nobody could
be gotten here in less than a year! You need to stay here to build up
a report--and you ought to be available for consultation when this
thing's to be done somewhere else! I'll report that I insisted as a
Survey emergency--"

Riki said confidently:

"Oh, that's all right! He'll do that! Of course! Won't you?"

Massy nodded dumbly. He thought, _I've been lonely all my life. I've
never belonged anywhere. But nobody could possibly belong anywhere
as thoroughly as I'll belong here when it's warm and green and even
the grass on the ground is partly my doing. But Riki'll like for me
still to be in the Service. Women like to see their husbands wearing
uniforms._

Aloud he said:

"Of course. It ... really needs to be done. Of course, you realize that
there's nothing really remarkable about it. Everything I've done has
been what I was taught, or read in books."

"Hush!" said Riki. "You're wonderful!"


                                THE END