284 Original Articles. [April, 



various atmospheric and other gases ; Prof. Tyndall having shown 

 that while oxygen, nitrogen, and some others, are, like rock-salt, 

 absolutely diathermic, and dry air nearly so, carbonic acid, marsh, 

 and olefiant gases, when compared with the latter as 1, possess 

 absorptive powers of 90, 403, and 970 respectively. Obviously, 

 therefore, the diffusion through the atmosphere of a considerable 

 quantity of either of these gases, which unlike aqueous vapour are 

 incapable of being deposited in a condensed state, would by prevent- 

 ing the dissipation of heat by radiation, keep up a high degree of 

 general warmth. Some such condition of atmosphere may have ex- 

 isted previous to, and during, the Carboniferous period. Another 

 cause, and one on which, from the proof that is obtainable of its 

 operation on other planets, greater stress must be laid, is varying 

 depths of atmosphere. Although the evaluation of the intensity of this 

 has been recently shown to be rather less definite than was supposed, 

 it is still sufficiently so to be made the basis of very important con- 

 clusions. The most general fact noticed by all scientific aeronauts, 

 from Gay-Lussac to Glaisher, is that there is a very marked diminu- 

 tion of temperature with ascent into the higher regions of the atmo- 

 sphere. The theoretical value usually assigned to the decrement is 

 1° for every 300 ft., and this was the actual value found by Mr.Welsh, 

 in 1822. Mr. Glaisher has come to the conclusion that this result is 

 generally true up to a height of 5,000 ft., when the sky is partially 

 cloudy, the diminution, however, even within these limits, being in a 

 greater ratio in the lower than in the higher strata. Above 5,000 ft. 

 he found the decrement reduced to 1° in every 1,000 ft. Gay-Lussac, 

 who ascended nearly 23,000 ft., found the temperature reduced from 

 82° on the surface to 15°. Mr. Hopkins, of Cambridge, has applied 

 these data to determine the question of how far different atmospheric 

 depths alone would affect the temperature of different planetary sur- 

 faces. According to the ordinary law of radiation the amount of heat 

 and light at Jupiter would be as 1 : 27 compared with that at the Earth. 

 If our planet, therefore, were moving in Jupiter's orbit with her present 

 physical arrangements, the mean annual temperature of her equator 

 would be — 34°-42 Fahr. ( — 36°-9 C), and at the pole a little more than 

 — 39°-l Fahr. (— 39°-5 C), and 35,000 or 40,000 ft. of our basic atmo- 

 sphere would elevate the equatorial heat to an equality with that of our 

 present temperate zones. At the other planets a proportionate addi- 

 tion or subtraction would be attended with proportionate effects. To 

 inquire now into the physical arrangements on Jupiter; telescopic 

 observations prove that the light from him is mostly reflected from 

 cloud-like masses above his svirface, the intensity of the whiteness of 

 this light exceeding that reflected from any known opaque substance, 

 and being far greater than that thrown off from an equal area of new 

 fallen snow, and fourteen times greater from any given space than 

 that from an equal surface on the full moon. If these masses should 

 be proved to be clouds they would afford unmistakable evidence of an at- 

 mosphere, though the depth would still remain unsettled. On both these 

 points, however, there is very satisfactory evidence. For, from the fact 

 that the dark lines in the solar spectrum increase as the sun's altitude 



