156 ANNUAL OF SCIENTIFIC DISCOVERY. 



would constantly increase, omitting variations due to temporary or local 

 causes. 



Thus it follows, that the existence of an atmosphere like that of the earth, 

 enveloping a planet, may, according to its extent, either elevate the superficial 

 temperature of the planet above, or depress it below that of surrounding 

 space independently of the direct solar radiation. "With respect to our own 

 globe, we are entirely ignorant of the height to which the thermometer, in 

 ascending, would continue to indicate a decreasing temperature, but we are 

 sure that such height is great. This is important with reference to the ulti- 

 mate object of this paper ; for if the height of a planet's atmosphere were too 

 small to allow a thermometer descending in it to attain its minimum indica- 

 tion, it is manifest that an increase of atmosphere would cause a decrease in 

 the planet's superficial temperature ; whereas, if the height of the atmosphere 

 were great enough to allow the thermometer to attain the minimum, any 

 increase of atmosphere would necessarily cause an increase in the superficial 

 temperature of the planet. 



In the earth's atmosphere, we are sure (as just remarked) that the indica- 

 tions of the thermometer would constantly increase in its descent from a very 

 high point above the earth's surface ; and therefore it follows, that if a planet 

 be enveloped in an atmosphere similar to that of the earth, supposing both 

 to exist in the planetary space unaffected by the heat which radiates from 

 the sun, the superficial temperature of the planet would necessarily be less, 

 under the same conditions, than that of the earth, if its atmosphere were 

 smaller, unless it should be so small as not to allow a thermometer descend- 

 ing in it to reach its minimum indication. If the planet were entirely with- 

 out atmosphere, its superficial temperature (in the assumed absence of solar 

 radiation) would be that of surrounding space ; but we have no means of 

 determining what relation that temperature bears to existing terrestrial tem- 

 perature, or what this latter temperature would become in the absence of 

 solar radiation. 



The author has calculated from Poisson's formulae, the increase of tempe- 

 rature in the superficial crust of the earth, due to the amount of heat received 

 by direct radiation from the sun, in different latitudes, above that temperature 

 which would be common to all parts of the earth's surface in the absence of 

 solar radiation, and with a uniformity of intensity of stellar radiation m all 

 directions upon our globe. 



But this increased temperature must produce an augmentation of tempera- 

 ture in the atmosphere, which must react on the terrestrial temperature till 

 equilibrium of temperature be established. The author has endeavored to 

 estimate the amount of this indirect effect of solar radiation by means of the 

 data furnished by M. Dove's work on terrestrial temperatures, combined with 

 calculations based on Poisson's formulas. He concludes that the whole effect 

 of solar heat at any proposed place is very nearly double that due to the 

 immediate and direct effect of solar radiation. 



Having thus ascertained this entire effect, he finds the temperature which 

 would pervade the whole surface of the earth if solar heat were extinguished. 

 He estimates this temperature at 39. 5 C. The annual variation of tempe- 



