Transcriber Note

Text emphasis is denoted as _Italics_. Whole and fractional parts of
number as 1234-56/789.




                               THE MOON

                                  BY

                         OLIVER C. FARRINGTON

                          CURATOR OF GEOLOGY


                            [Illustration]


                                GEOLOGY

                               LEAFLET 6


                    FIELD MUSEUM OF NATURAL HISTORY

                                CHICAGO

                                 1925


LIST OF GEOLOGICAL LEAFLETS ISSUED TO DATE

  No. 1.  Model of an Arizona Gold Mine                              $ .10

  No. 2.  Models of Blast Furnaces for Smelting Iron                   .10

  No. 3.  Amber--Its Physical Properties and Geological Occurrence     .10

  No. 4.  Meteorites                                                   .10

  No. 5.  Soils                                                        .10

  No. 6.  The Moon                                                     .10

                                         D. C. DA VIES, DIRECTOR

  FIELD MUSEUM OF NATURAL HISTORY
        CHICAGO. U.S.A.

[Illustration: LEAFLET 6. PLATE I.

PHOTOGRAPH OF MODEL IN RELIEF OF THE VISIBLE HEMISPHERE OF THE MOON.
HALL 35.

The model is 19 feet in diameter.]


                    FIELD MUSEUM OF NATURAL HISTORY

                         DEPARTMENT OF GEOLOGY

                             CHICAGO, 1925

  ------------------------------------------------------------
  LEAFLET                                             NUMBER 6
  ------------------------------------------------------------

                           Table of Contents

   The Moon                                               1
   General Observations.                                  7
   Description of Individual Features. 	                  7
   Sources of Additional Information About the Moon.     13




THE MOON


Except for occasional comets and meteors, the Moon is the celestial
body nearest the Earth. Its mean distance from the Earth is 237,640
miles, but as it moves in an elliptical orbit, it has at one point
a remoteness of 253,263 miles and opposite to this one of 221,436
miles. The diameter of the Moon is about one-fourth that of the Earth,
or 2,160 miles, and its volume is 1/49 that of the Earth. The mass
of the Moon (volume multiplied by density) is 1/81 and the density
⅗ that of the Earth. The period of the Moon's revolution about the
Earth is 27 days, 7 hours, 43 minutes and 11½ seconds. As its period
of rotation on its axis is the same, only one side of the Moon is ever
seen from the Earth. Since, however, the Moon's axis is inclined about
83° to the plane of its orbit, we sometimes see a little distance
beyond each of its poles, and, since the rate of motion of the Moon
in its orbit varies slightly, we sometimes see a little beyond the
eastern and western edges of the hemisphere. The total result of these
_librations_, as they are called, is to make four-sevenths of the
Moon's surface visible to us. Of the remaining three-sevenths, nothing
is known. So far as is known, the Moon is not flattened at the poles.

Owing to its slow rotation on its axis, the Moon's day has a length of
29½ of our days. Each portion of its surface is therefore exposed to or
shielded from the light of the Sun for a fortnight continuously.

The Moon has no atmosphere. Hence, it can have no diffused light, and
nothing can be seen on it except where the Sun's rays shine directly.
"If a man stepped into the shadow of a lunar crag," says Todd, "he
would instantly become invisible. For a similar reason, no sound,
however loud, can be heard on the Moon. The rolling of a rock down the
wall of a lunar crater, will be known only by the tremor it produces."
Moreover, changes of temperature on the Moon are rapid and violent.
Where the Sun's rays strike, a temperature about that of boiling water
is believed to be reached, while in unilluminated portions it is
thought to go as low as 100° below zero.

The force of gravity upon the surface of the Moon is only ⅙ of that on
the Earth. Therefore, a man weighing 150 pounds on the Earth, would
weigh only 25 pounds on the Moon, and the same muscular energy by which
he could jump 6 feet on the Earth would carry him a distance of 36 feet
on the Moon. On the Earth a body falls 16 feet in one second; on the
Moon only 2.6 feet in the same time.

The surface of the Moon is made up of mountains, valleys and plains,
resembling in general appearance those of the Earth. As a whole,
however, the surface of the Moon is much more uneven than that of the
Earth. Some of the mountains of the Moon have a height of over 20,000
feet. As there is no sea-level to measure from, this figure expresses
height above the surrounding surface, it being determined by the length
of the shadows cast by the mountains.

In order to represent in a vivid and accurate manner the character and
appearance of the Moon's surface, the construction of a large model of
the Moon was undertaken a number of years ago by Th. Dickert, Curator
of the Natural History Museum of Bonn, Germany and Dr. J. F. Julius
Schmidt, Director of the Observatory of Athens, Greece and an eminent
selenographer. The model was presented to the Museum by the late Lewis
Reese of Chicago, and is installed at the west end of Hall 35 of the
Museum. The model is 19.2 feet in diameter, and is by far the largest
and most elaborate representation of the Moon's surface ever made. Its
horizontal scale is 1:600,000, one inch on the model equaling 9-47/100
miles on the surface of the Moon, and its vertical scale is 1:200,000,
one inch equaling 3-15/100 miles on the Moon.

Some characteristic features of the Moon's surface which are especially
well illustrated on the model are the following:

1. GRAY PLAINS or "SEAS." These are the darker portions of the Moon's
surface as it is seen with the naked eye. They were thought by earlier
observers to be seas and were so named. We now know, however, that
there is no water on the Moon's surface and that the so-called "seas"
are really low-land plains, some of them of vast extent. The Oceanus
Procellarum, for instance, covers an area of 90,000 square miles.
As seen from the Earth, the plains show a gray-green color, often
of varying intensity and sometimes a little bluish in portions. The
brightest green color is shown by the area known as Mare Serenitatis.
Though appearing perfectly level, a close study shows that these plains
have undulating surfaces. They occupy about one-third of the visible
surface of the Moon.

2. MOUNTAINS and HIGHLANDS. These constitute the bright portions of the
Moon's surface as it is seen with the naked eye.

Although these elevated areas are conveniently called mountains, Shaler
has drawn attention to the fact that they are unlike those on the
Earth since they lack features due to erosion and there is absence of
order in their association. The average declivity of their slopes is
also much greater than that of the mountains on the Earth. It has been
estimated that the average angle of the lunar surface to its horizon is
52°, while on the Earth it does not amount to more than one-tenth of
that figure. This difference is probably due to the lack of water on
the Moon, the work of which on the Earth tends continually to reduce
slopes to a level. Using the term mountains for convenience, however,
those on the Moon may be divided into the following classes:

_a._ MOUNTAIN CHAINS. These may have a length of 80 to 100 miles and
heights of from 5,000 to 17,000 feet. As in the case with the mountains
of the Earth, they are usually steeper on one side than on the other.
The range called the Appenines, seen near the north pole of the Moon,
is a good illustration of such mountain chains. Other ranges are the
so-called Alps and Caucasus. These names were applied by Hevelius, an
astronomer of Danzig, who made the first map of the Moon in 1647. He
gave to the features of the Moon's surface names of localities similar
to those on the Earth which they most resembled. His system was largely
abandoned by later astronomers, however, the later method being to name
the different features of the Moon after celebrated astronomers and
philosophers.

_b._ HIGHLANDS SURROUNDED BY MOUNTAINS. These are partly with and
partly without well-determined directions.

_c._ ISOLATED MOUNTAINS. These usually occur on the gray plains. They
vary from 4,000 to 7,000 feet in height.

_d._ VEIN MOUNTAINS. These occur only on the gray plains. They are
long, narrow, contorted ridges, usually from 700 to 1,000 feet in
height.

_e._ CIRCULAR MOUNTAINS. These are the most characteristic and peculiar
features of the Moon's surface. They vary in size from the so-called
"Walled Plains," 150 to 15 miles in diameter, to crater mountains whose
diameters range from 15 miles down to a few hundred feet. Thirty-three
thousand of these crater mountains have been counted by one astronomer,
the number increasing as the size diminishes.

The form of these craters is that of pits, which generally have
ring-like walls about them. These wails slope very steeply to a central
cavity and more gently toward the surrounding country. In all these
pits, as pointed out by Shaler, except those of the smallest size,
and possibly in these, also, there is, within the ring wall and at a
considerable though variable depth below its summit, a nearly flat
floor, which often has a central pit of small size or, in its place,
a steep cone. When this floor is more than 20 miles in diameter, and
in increasing numbers as it is wider, there are generally other pits
and cones irregularly scattered upon it. Thus, within the ring called
Plato, which is about 60 miles in diameter, there are some scores of
these lesser pits. On the interior of the ring walls of the pits over
10 miles in diameter, there are usually more or less distinct terraces,
which suggest that the material now forming the solid floors they
inclose was once fluid and stood at greater heights in the pit than
that at which it became permanently frozen. It is, indeed, tolerably
certain that the last movement of this material of the floors was one
of interrupted subsidence from an originally greater elevation on
the outside of the ring wall. The ring wall is commonly of irregular
height, with many peaks. In some places there may be seen tongues or
protrusions of the substance which forms the ring, as if it had flowed
a short distance and then had cooled with steep slopes. It may also
be noted: (_a_) that the pits or craters in many instances intersect
each other, showing that they were not all formed at the same time,
but in succession; (_b_) that the larger of them are not found on the
plains (seas) but on the upland and apparently the older parts of the
surface; and (_c_) that the evidence from the intersections clearly
indicates that the larger of these structures are prevailingly the
older and that in general the smallest were the latest formed. In other
words, says Shaler, whatever was the nature of the action involved in
the production of the craters, its energy diminished with time, until
in the end it could no longer break the crust. These features indicate
that the surface of the Moon has been subject to forces similar to
those which produce volcanoes on the Earth, and it is therefore
customary to refer to the crater-like mountains of the Moon as
volcanoes. As the parallel cannot be drawn too closely, however, Shaler
has urged that the term vulcanoids, meaning volcano-like, be applied to
these mountains.

3. RILLS or CLEFTS. These are small, deep, ditch-like furrows to be
found over various parts of the Moon's surface. Their course seems
quite independent of the surface topography, for they traverse
mountains and plains with equal facility. They are without doubt the
latest formation on the Moon and some of them may have had their origin
in modern times.

4. BRIGHT STREAKS. These radiate prominently from many of the great
craters of the Moon. They are streaks of narrow width but sometimes
nearly a hundred miles in length. They are perhaps the most puzzling
of all the Moon's features. They have been supposed by some observers
to represent lava flows whose surface reflected light more brilliantly
than other portions of the Moon. It is more generally believed,
however, that the streaks do not represent any independent elevations,
since they run over the highest mountains as well as through the
deepest craters without variation.




GENERAL OBSERVATIONS.


The condition of the Moon's surface as a whole indicates that it has
been a theater of extraordinary volcanic activity. In size and number
its vulcanoids far exceed the volcanoes of the Earth. The largest
terrestrial crater known is that of Kilauea in the Hawaiian Islands
which is 2½ miles in diameter. Several craters of the Moon, however,
exceed 50 miles in diameter and one measures 114¼ miles. While the
absolute heights of the mountains of the Moon do not greatly exceed
those of the Earth, proportionally they are much higher, since the
Moon's diameter is only one-fourth that of the Earth. The vulcanoids
of the Moon differ in other respects from the volcanoes of our globe.
"On the Earth they are usually openings on the summits or sides of
mountains--on the Moon, depressions below the adjacent surface even
when it is a plain or valley; on the Earth the mass of the cone usually
far exceeds the capacity of the crater--on the Moon they are much
nearer equality; on the Earth they are commonly the sources of long
lava streams--on the Moon, traces of such outpourings are rare." (Webb.)




DESCRIPTION OF INDIVIDUAL FEATURES.

(Abridged from Nasmyth and Carpenter.)

The numbers refer to those on the accompanying chart.


COPERNICUS. 147. This may deservedly be considered one of the grandest
and most instructive of lunar craters. Though its diameter (46 miles)
is exceeded by that of other craters, its situation near the center
of the lunar disc renders it so conspicuous as to make it a favorite
object for observation. Its vast rampart rises to upwards of 12,000
feet above the level of the plateau, nearly in the center of which
stands a magnificent group of cones attaining the height of upwards
of 2400 feet. The rampart is divided by concentric segmented terraced
ridges, which present every appearance of being enormous landslips,
resulting from the crushing of their overloaded summits which have
slid down in vast segments and scattered their debris on the plateau.
Corresponding vacancies in the rampart may be observed from whence
these prodigious masses have broken away. The same may be noticed, to
a somewhat modified degree, around the exterior of the rampart. For
upwards of 70 miles around Copernicus myriads of comparatively minute
but perfectly formed craters can be seen. The district on the southeast
side is especially rich in them. Many somewhat radial ridges or spurs
may be observed leading away from the exterior banks of the great
rampart. They appear to be due to the freer egress which the extruded
matter found near the focus of disruption.

TRIESNECKER. 150. A fine example of a normal lunar volcanic crater
having all the usual characteristic features in great perfection.
Its diameter is about 20 miles and it possesses a good example of
the central cone and also of interior terracing. The most notable
feature, however, is the remarkable display of cracks or chasms which
may be seen to the west side of it. Several of these cracks obviously
diverge from near the west external bank of the great crater and they
sub-divide or branch out as they extend from the apparent point of
divergence, while they are crossed or intersected by others. These
cracks or chasms are nearly one mile wide at their widest part and
after extending for fully 100 miles taper away till they become
invisible.

THEOPHILUS. 97. CYRILLUS. 96. CATHARINA. 95. These three magnificent
craters form a conspicuous group. Their diameters and depths are as
follows: Theophilus, diameter, 64 miles; depth of interior plateau
from summit of crater wall, 16,000 feet; central cone, 5200 feet high;
Cyrillus, diameter, 60 miles; depth of interior plateau from summit
of crater wall, 15,000 feet; central cone, 5800 feet high; Catharina,
diameter, 65 miles; depth of interior plateau from summit of crater
wall, 13,000 feet; center of plateau occupied by a confused group of
minor craters and debris. Each of these craters is full of interesting
details presenting in every variety the characteristic features of the
lunar volcanoes and giving unmistakable evidence of the tremendous
energy which at some remote period piled up such gigantic formations.
The intrusion of Theophilus within Cyrillus shows that it is of more
recent formation than the latter. The flanks of Theophilus, especially
on the west side, are studded with apparently minute craters. These
would be considered of great size but for the enormous crater so near.

PTOLEMY. 111. ALPHONS. 110. ARZACHAEL. 84. The portion of the moon's
surface which includes these features, being near the center of the
lunar disc, is exceptionally well placed for observation. Within
this area may be seen every variety of volcanic craters and a number
of other interesting forms. Ptolemy belongs to the class of walled
plains, its ramparts enclosing a plain 86 miles in diameter. Alphons
and Arzachael are respectively 60 and 55 miles in diameter. They have
all the distinctive features of lunar craters, viz:--central cones,
lofty, ragged ramparts, manifestations of landslip formations in the
great segmental terraces within their ramparts and minor craters
interpolated within their plateaus. A notable object near Alphons is
an enormous straight cliff traversing the diameter of a low, ridged,
circular formation. This great cliff is 60 miles long and from 1000 to
2000 feet high. It is a well known object to lunar observers and has
been termed "The Railway" on account of its straightness. The existence
of this remarkable cliff appears to be due either to an upheaval or a
down-sinking of a portion of the surface of the circular area across
whose diameter it extends.

TYCHO. 80. This magnificent crater is 54 miles in diameter and upwards
of 16,000 feet deep from the highest ridge of the rampart to the
surface of the plateau. It is one of the most conspicuous of lunar
craters, not so much on account of its dimensions as from its occupying
the great focus of disruption from whence diverge those remarkable
bright streaks many of which may be traced over 1000 miles of the
moon's surface. The interior of the crater presents striking examples
of the concentric, terrace-like formations that are regarded as formed
by landslips.

WARGENTIN. 26. SCHICKARD. 28. Wargentin is an object quite unique of
its kind--a crater about 52 miles across, that to all appearance has
been filled to the brim with lava that has been left to consolidate.
There are evidences of the remains of a rampart, especially on the
southwest portion of the rim. The general aspect of Wargentin has been
compared to that of a "thin cheese." The terraced and rutted exterior
of the rampart has all the details of a true crater. The surface of
the high plateau is marked by a few ridges branching from a point
nearly in the center.

Schickard is one of the finest examples of a walled plain. It is 153
miles in diameter. Within its rampart are 16 smaller craters and
without, numberless others.

The following are the names of topographic features of the Moon which
can be located by the corresponding numbers on the accompanying chart.

    1. Newton.                59. Pontanus.
    2. Short.                 60. Poisson.
    3. Simpelius.             61. Aliacensis.
    4. Manzinus.              62. Werner.
    5. Moretus.               63. Pitatus.
    6. Gruemberger.           64. Hesiodus.
    7. Casatus.               65. Mercator.
    8. Klaproth.              66. Vitello.
    9. Wilson.                67. Fourier.
   10. Kircher.               68. Lagrange.
   11. Bettinus.              69. Vieta.
   12. Blancanus.             70. Doppelmayer.
   13. Clavius.               71. Campanus.
   14. Scheiner.              72. Kies.
   15. Zuchius.               73. Purbach.
   16. Segner.                74. La Caille.
   17. Bacon.                 75. Playfair.
   18. Nearchus.              76. Azophi.
   19. Vlacq.                 77. Sacrobosco.
   20. Hommel.                78. Fracastorius.
   21. Licetus.               79. Santbech.
   22. Maginus.               80. Petavius.
   23. Longomontanus.         81. Wilhelm Humboldt.
   24. Schiller.              82. Polybius.
   25. Phocylides.            83. Geber.
   26. Wargentin.             84. Arzachael.
   27. Inghirami.             85. Thebit.
   28. Schickard.             86. Bullialdus.
   29. Wilhelm I.             87. Hippalus.
   30. Tycho.                 88. Cavendish.
   31. Saussure.              89. Mersenius.
   32. Stoefler.              90. Gassendi.
   33. Maurolycus.            91. Lubiniezky.
   34. Barocius.              92. Alpetragius.
   35. Fabricius.             93. Airy.
   36. Metius.                94. Almanon.
   37. Fernelius.             95. Catharina.
   38. Heinsius.              96. Cyrillus.
   39. Hainzel.               97. Theophilus.
   40. Bouvard.               98. Colombo.
   41. Piazzi.                99. Vendelinus.
   42. Ramsden.              100. Langreen.
   43. Capuanus.             101. Goclenius.
   44. Cichus.               102. Guttemberg.
   45. Wurzelbauer.          103. Isidorus.
   46. Gauricus.             104. Capella.
   47. Hell.                 105. Kant.
   48. Walter.               106. Descartes.
   49. Nonius.               107. Abulfeda.
   50. Riccius.              108. Parrot.
   51. Rheita.               109. Albategnius.
   52. Furnerius.            110. Alphons.
   53. Stevinus.             111. Ptolemy.
   54. Hase.                 112. Herschel.
   55. Snell.                113. Davy.
   56. Borda.                114. Guerike.
   57. Neander.              116. Bonpland.
   58. Piccolomini.

  117. Lalande.              174. Seleucus.
  118. Reaumur.              175. Herodotus.
  120. Letronne.             176. Aristarchus.
  121. Billy.                177. La Hire.
  122. Fontana.              178. Pytheas.
  123. Hansteen.             179. Bessel.
  124. Damoiseau.            180. Vitruvius.
  125. Grimaldi.             181. Maraldi.
  126. Flamsteed.            182. Macrobius.
  127. Landsberg.            183. Cleomides.
  128. Moesting.             184. Roemer.
  129. Deambrel.             185. Littrow.
  130. Taylor.               186. Posidonius.
  131. Messier.              187. Geminus.
  132. Maskelyne.            188. Linnaeus.
  133. Sabine.               189. Autolycus.
  134. Ritter.               190. Aristillus.
  135. Godin.                191. Archimedes.
  136. Soemmering.           192. Timocharis.
  137. Schroeter.            193. Lambert.
  138. Gambart.              194. Diophantus.
  139. Reinhold.             195. Delisle.
  140. Encke.                196. Briggs.
  141. Hevelius.             197. Lichtenberg.
  142. Riccioli.             199. Calippus.
  143. Lohrman.              200. Cassini.
  144. Cavalerius.           201. Gauss.
  145. Reiner.               202. Messala.
  146. Kepler.               203. Struve.
  147. Copernicus.           204. Mason.
  148. Stadius.              205. Plana.
  149. Pallas.               206. Burg.
  150. Triesnecker.          207. Baily.
  151. Agrippa.              208. Eudoxus.
  152. Arago.                209. Aristotle.
  153. Taruntius.            210. Plato.
  154. Apollonius.           211. Pico.
  155. Schubert.             212. Helicon.
  156. Firmicus.             213. Maupertuis.
  157. Silberschlag.         214. Condamine.
  158. Hyginus.              215. Bianchini.
  159. Ukert.                216. Sharp.
  160. Boscovich.            217. Mairan.
  161. Ross.                 218. Gerard.
  162. Proclus.              219. Repsold.
  163. Picard.               220. Pythagoras.
  164. Condorcet.            221. Fontenelle.
  165. Pliny or Menelaus.    222. Timaeus.
  167. Manilius.             223. Epigenes.
  168. Erastothenes.         224. Gartner.
  169. Gay Lussac.           225. Thales.
  170. Tobias Mayer.         226. Strabo.
  171. Marius.               227. Endymion.
  172. Olbers.               228. Atlas.
  173. Vasco de Gama.        229. Hercules.


                                   OLIVER C. FARRINGTON.




SOURCES OF ADDITIONAL INFORMATION ABOUT THE MOON


A number of textbooks and popular works on astronomy deal more or less
fully with the Moon. Among them the following may be mentioned.

  MOULTON, FOREST RAY--Introduction to Astronomy. Macmillan
  & Co., New York. 1916. 577 pp.

  YOUNG, CHARLES A.--A Textbook of General Astronomy. Ginn
  & Co., Boston. 1898. 630 pp.

  TODD, DAVID P.--Stars and Telescopes. Little, Brown & Co.,
  Boston. 1899. 419 pp.

The following are some works which treat exclusively of the Moon.

  NASMYTH, JAMES and CARPENTER, JAMES--The Moon. John
  Murray, London. 1885. 213 pp. 25 "Woodburytype"
  plates and several text figures.

  PICKERING, WILLIAM H.--The Moon. Doubleday, Page & Co.,
  New York. 1903. Quarto. 103 pp. and many full-sized
  plates.

  PROCTOR, RICHARD A.--The Moon. Longmans, Green & Co.,
  London. 1898. 314 pp.

  GILBERT, GROVE K.--The Moon's Face. Bulletin of the Philosophical
  Society of Washington, 1892-93. Vol. 12, pp.
  241-292.

  SHALER, NATHANIEL S.--A Comparison of the Features of the
  Earth and the Moon. Smithsonian Contributions to Knowledge.
  1907. Vol. 34, pp. 1-79. 25 plates.


[Illustration: LEAFLET 6. PLATE II.

CHART OF THE MOON'S SURFACE. AFTER NASMYTH.

The figures refer to the names given on pp. 11 and 12 and the use of
the chart with the model will enable the reader to name the different
features of the moon.]


PRINTED BY FIELD MUSEUM PRESS


       *       *       *       *       *


Transcriber Note

The list of "topographic features" (pp. 11-12) have some numbers
missing (115, 116) and a comparison with Nasmyth and Carpenter's The
Moon was missing those numbers but several other numbers were repeated.
The repeated numbers appear to represent craters too close to split out.