Page:The American Cyclopædia (1879) Volume XI.djvu/818

800 MOON of the apsides, are due to the disturbing action of the sun. The moon's surface has no obvious indications of water, nor of an atmosphere. Mr. C. B. Boyle of New York, however, who has long made a special study of the moon, main- tains that she has a slight atmosphere, and that she has also water in the shape of numerous small ponds, which for optical reasons are not always visible through the telescope, but have occasionally been noticed by astronomers as bright sparkling points. Schroter (about 1800) claimed to have discovered indications of vege- tation on the surface of the moon. These con- sist of certain traces of a greenish tint which appear and reappear periodically ; much as the white spots covering the polar regions of Mars, supposed to be snow and ice, are observed to increase in the winter and waste in the sum- mer of those regions of the planet. As we are able, under the most favorable conditions, to use upon the moon telescopic powers which have the effect of bringing the satellite to within 150 to 120 m. of us, we should doubtless notice any such marked changes on her surface as the pas- sage of the seasons produces, for example, on our own globe. In the most powerful instru- ments yet constructed the surface of the moon presents a scene of wildest desolation. In every direction are circular caverns or pits, many of enormous size ; the floor of one is seen to be strewn with huge blocks. The inner walls are commonly steep, and their depth often fright- ful, being many thousand feet. They are sur- rounded by annular ridges, the masses of which would exactly fill the enclosed cavities. In the centre commonly rises a conical mountain. All Moon at the First Quarter, from Photographs taken by Prof. H. Draper, New York. this plainly points to a volcanic origin. There are large regions perfectly level, which Sir John Herschel considered to be of a decided alluvial character. There are great rings of mountains enclosing areas of 40 to 120 m. in diameter. From these ranges shoot up stupendous peaks, one to the height of 16,000 ft. Isolated peaks here and there rise abruptly from extended plains to the height of 6,000 to 7,000 ft. These elevations are determined by calculations based on the height of the sun above the horizon of the lunar place under inspection, and the length of the shadows cast. The most favorable time for observing these remarkable features is when the moon is about half full. Beyond the illuminated hemisphere mountain peaks, rising miles above the average level of the surface, are then bathed in sunlight, while the intermediate space is veiled in darkness. Thus the peaks are at such a time seen as sil- ver points detached from the bright crescent ; or, if they form a chain stretching toward the rising sun, they may appear as ragged promon- tories of light jutting far out into the darkness. An admirable chart of the moon has been con- structed by the eminent Prussian observers, Beer and Madler, whose work, Der Mond, must be consulted for a full account of the physical condition of our satellite. They place the height of one mountain at 23,823 ft. This, considering the relative magnitudes of the moon and the earth, is far more stupendous than any known elevation of terrestrial sur- face. More recently Schmidt of Athens, Greece, has made an elaborate series of observations, extending over the years 1839-' 72. The diame- ter of the chart constructed from these obser- vations is to be six Paris feet, and it is to be published in 25 sections. The application of photography to the moon, though it has not yet resulted in giving maps comparable in ac- curacy of detail with those by Beer and Mad- ler, and by Schmidt, has yet given pictures of extreme value and interest. In 1840 Dr. J. W. Draper of New York first succeeded in photo- graphing the moon. With a telescope 5 in. in aperture he obtained pictures on silver plates, and presented them to the lyceum of natural history of New York. Bond of Cambridge, Mass., made photographic pictures 2 in. in diameter with the refractor of the Harvard observatory in 1850. Since then, Secchi in Rome, Bertch and Arnauld in France, and Phillips, Hartnup, Crookes, De la Rue, and others in England, have made lunar photo- graphs, some of those by De la Rue being ad- mirable. Dr. H. Draper and Mr. Rutherfnrd of New York have taken some of the finest pho- tographic views yet produced. To one of the photographs by Rutherfurd (taken Feb. 27, 1871) De la Rue ascribes the palm of absolute superiority among all the lunar photographs yet taken. The mass of the moon is not accu- rately known, though the most trustworthy determinations agree in placing it at about ^f T part of the mass of the earth. The mass of the moon is intimately associated with her dis- tance and motions. It is best determined from the nutation of the earth's axis (see NUTA- TION), and when determined must be added to the earth's mass in calculating the deflecting action of the mutual gravitation of the earth