COSMICAL GEOLOGY. l6l 



bands are visible at both sides of the equator, and a number 

 of smaller streaks run parallel to them. An elliptical red spot 

 can also be seen. From these observations it would appear 

 that this planet is encircled by a mantle of cloud or by floating 

 layers of vapour, through which the still incandescent nucleus 

 shows itself as a red spot. Saturn displays a surface similar to 

 that of Jupiter ; its remarkable ring was explained by Kant as 

 a vaporous mass composed of infinitely fine particles. The 

 two outermost planets are too remote from the Earth to permit 

 of detailed telescopic examination. 



As regards the spectra of the planets, Fraunhofer had 

 determined their agreement with the sun's spectrum, and in 

 more recent years the spectroscope has shown that for the 

 most part the planets only reflect the sun's rays. 



If one may venture to draw conclusions from these 

 observations, Mars with its thin atmosphere may probably be 

 regarded as the planet most akin to the Earth. Mars, and 

 possibly Venus, with its thick cloud-mantle, are the only 

 planets upon which living creatures could be supposed to 

 exist. Life must be impossible on Mercury on account of its 

 proximity to the sun ; Jupiter and Saturn radiate light of their 

 own to a certain degree, and are probably still in an incan- 

 descent state. The spectra of Uranus and Neptune would 

 seem to indicate a condition of incomplete consolidation, and 

 the low density of these planets is an additional fact in favour 

 of this hypothesis. 



The Moon. The moon is the heavenly body which has 

 been examined by astronomers in greatest detail. This has 

 been rendered possible by its relatively small distance from 

 the earth, the absence of water or clouds, as well as by the 

 absence or very slight development of an atmosphere on the 

 side f the moon which is exposed to us. Although classical 

 literature contains scattered observations regarding the moon's 

 surface, the cartography of the moon was not attempted until 

 the telescope came into use. Then Galilei and other astro- 

 nomers of the seventeenth century made sketches of the 

 moon's surface. In the middle of the eighteenth century 

 Professor Tobias Mayer projected a topographical map of the 

 moon on the basis of measurements, the precision of which 

 far surpassed previous attempts. In the earlier part of this 

 century several astronomers published maps and reliefs of the 



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