226 ATMOSPHERES OF THE PLANETS. SECT. XXV. 



The climate of Venus more nearly resembles that of the earth, 

 though, excepting at her poles, much too hot for animal and 

 vegetable life such as they exist here, for she receives seven times 

 as much light and heat as the earth does ; but in Mercury the 

 mean heat from the intensity of the sun's rays must be above 

 that of boiling quicksilver, and water would boil even at his 

 poles. Thus the planets, though kindred with the earth in 

 motion and form, are, according to our experience, totally unfit 

 for the habitation of such a being as man, unless indeed their 

 temperature should be modified by circumstances of which we 

 are not aware, and which may increase or diminish the sensible 

 heat so as to render them habitable. In our utter ignorance it 

 may be observed, that the earth, if visible at all from Neptune, 

 can only be a minute telescopic object ; that from the nearest fixed 

 star the sun must dwindle to a mere point of light ; that the 

 whole solar system would there be hid by a spider's thread ; and 

 that the starry firmament itself is 'only the first series of starry 

 systems, the numbers of which are bounded alone by the imper- 

 fection of our space-penetrating instruments. In this overwhelm- 

 ing majesty of creation, it seems rash to affirm that the earth 

 alone is inhabited by intelligent beings, and thus to limit the 

 Omnipotent, who has made nothing in vain. 



Several of the planets have extensive and dense atmospheres : 

 according to Schroeter the atmosphere of Ceres is more than 668 

 miles high, and that of Pallas has an elevation of 465 miles, but 

 not a trace of an atmosphere can be perceived round Vesta. The 

 attraction of the earth has probably deprived the moon of hers, 

 for the refractive power of the air at the surface of the earth is at 

 least a thousand times as great as at the surface of the moon: the 

 lunar atmosphere must therefore be of a greater degree of rarity 

 than can be produced by our best air-pumps. This is confirmed 

 by Arago's observations during a solar eclipse, when no trace of a 

 lunar atmosphere could be seen. Since then, however, some 

 indications of air have been perceived in the lunar valleys. In 

 taking photographic images of the moon and Jupiter at Rome, 

 Professor Secchi found that the light of the full moon is to that 

 of the quarter moon as 3 to 1. Jupiter gives a photographic 

 image as bright and vigorous as the brightest part of the moon ; 

 but although the light of Jupiter is less than that of the moon, 

 he is nearly five times farther from the sun ; and as light 



