SOLAR LIGHT AND HEAT. 



the possibility of the existence of water in the liquid state on the 

 moon, that, in the absence of an atmosphere, the temperature 

 must necessarily be, not only far below the point of congelation 

 of water, but even that of most other known liquids. Even 

 within the tropics, and under the line with a vertical sun, the 

 height of the snow line does not exceed 16000 feet, and never- 

 theless at that elevation, and still higher, there prevails an atmo- 

 sphere capable of supporting a considerable column of mercury. 

 At somewhat greater elevations, but still in an atmosphere of 

 very sensible density, mercury is congealed. Analogy, therefore, 

 justifies the inference that the total, or nearly total, absence of air 

 upon the moon is altogether incompatible with the existence of 

 water, or probably any other body in the liquid state, and neces- 

 sarily infers a temperature altogether incompatible with the 

 existence of organised beings in any respect analogous to those 

 which inhabit the earth. 



But another conclusive evidence of the non-existence of liquids 

 on the moon is found in the form of its surface, which exhibits 

 none of those well understood appearances which result from the 

 long-continued action of water. The mountain formations with 

 which the entire visible surface is covered are, as will presently 

 appear, universally so abrupt, precipitous, and unchangeable, as 

 to be utterly incompatible with the presence of liquids. 



15. The general diffusion of the sun's light upon the earth is 

 mainly due to the reflection and refraction of the atmosphere, 

 and to the light reflected by the clouds ; and without such means 

 of diffusion the solar light would only illuminate those places into 

 which its rays would directly penetrate. Every place not in full 

 sunshine, or exposed to some illuminated surface, would be 

 involved in the most pitchy darkness. The sky at noon-day 

 would be intensely black, for the beautiful azure of our firmament 

 in the day-time is due to the reflected colour of the air. Thus it 

 appears that the absence of air on the moon must deprive the 

 sun's illuminating and heating agency of nearly all its utility. 



16. If the moon were inhabited, observers placed upon it would 

 witness celestial phenomena of a singular description, differing 

 in many respects from those presented to the inhabitants of our 

 globe. The heavens would be perpetually serene and cloudless. 

 The stars and planets would shine with extraordinary splendour 

 during the long night of 328 hours. The inclination of her axis 

 being only 5, there would be no sensible changes of season. The 

 year would consist of one unbroken monotony of equinox. The 

 inhabitants of one hemisphere would never see the earth : while 

 the inhabitants of the other would have it constantly in their 

 firmament by day and by night, and always in the same position. 



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