AND THE OTHER PLANETS OF THE SOLAR SYSTEM. . 659 



I have hitherto spoken of a and b as two constants to be determined by observation 

 (Art. 18), but it is important to consider their physical meaning. Now 



a 2 = - , and b = - , 

 c k 



where k = the conductivity of the matter of the Earth's crust near to its surface ; 



c = its specific heat ; 



p = the transmitting power of the Earth's surface. 



Hence, 



1 ck 



oV = / ; 



c 

 and, therefore, if the ratio — of the specific heat to the transmitting power of the surface, 



k . . 1 



or the ratio - of the conductivity to the same power, be increased, — will be increased, 

 p ab 



as will also, therefore, — and — - . Consequently the coefficients of the two periodical in- 

 equalities above mentioned will be diminished. This ought manifestly to be the case ; for 

 if a given quantity of heat pass in a given time into a planet, for example, through a given 

 area of its surface, the effect on the temperature of the matter into which it passes will be the 

 less, the greater the specific heat of that matter ; and the greater its conductivity, the more 

 rapidly will the incident heat be carried away downwards, and the less will be its effect in raising 

 the superficial temperature. In this latter case, the amplitude of the inequality, or the depth 

 to which it would sensibly extend, would be increased, but its magnitude at the surface would 

 be diminished. It is obvious how much periodical inequalities in the superficial temperature 

 of a body like the Earth, and therefore also in the temperature of the lowest stratum of its 

 atmosphere, might be modified by an adaptation of the specific heat and conductivity of the 

 matter composing it, and the transmissive power of its surface, to the conditions under 

 which it may be placed. 



28. It may be well to give a brief summary of the previous portions of this paper 

 before I proceed to apply the results obtained with reference to the Earth to the other 

 planets of the solar system. 



(1) I have endeavoured to explain, as fully as possible, the manner in which 

 the atmosphere produces its influence on the temperature of the Earth's surface ; and to 

 shew that the temperature of the constituent particles of the atmosphere at its upper limit 

 must be exceedingly low. 



(2) If as much atmosphere were removed from the Earth as now forms an inferior 

 stratum of about 525 feet in thickness, the mean annual temperature of each point on the 

 Earth's surface would be diminished by 1° (C). In different latitudes at the same period 

 of the year, and in different seasons at the same place the thickness of the stratum of 

 atmosphere corresponding to 1° (C) would be somewhat different, being probably somewhat 



