664 Mr W. HOPKINS, ON THE EXTERNAL TEMPERATURE OF THE EARTH, 



The coefficient of the annual inequality for any latitude, supposing — to be constant, 



depends upon the value of h sin y (Art. 20), (y being the obliquity). Now in the case of the 



Earth 



h sin 7 = 14°,33 (C); 



and in the case of Mars 



h sin y = 7°,68 ; 



and hence the coefficient of the inequality, which in the case of the Earth 



= ± 16°,44 sin ^ 

 becomes in the case of Mars, 



= ± 8°,71 sin ix. 



Consequently the variations of temperature in different seasons of Mars would little exceed half 



b ck 



the corresponding variations on the Earth, assuming — , or the ratio — r , to be the same in 



P 

 both planets (Art. 27). If it be different, the values of this inequality in Mars and the Earth 



must bear a different ratio to each other. We may remark, however, that the least value of 



D b 1 ck 



— and, therefore, the greatest value of — is unity, to which it approximates as — — or — 



approximates to zero. Now the value of - for the Earth, as above given (Art. 25), is ,731. 



Consequently, the annual inequality of temperature, so far as it depends on the conductivity 

 and specific heat of the superficial matter of the planet, and the transmissive power of its 

 surface, cannot be much greater in any other planet than in our own globe. On the other 



hand, it may be diminished in any ratio by the increase of the quantity — . 



33. Let us now take the case of Venus. Her distance from the Sun is such that the 

 intensity of the solar radiation must be very nearly twice that at the distance of the Earth. 

 Hence we may take generally, 



h = 70° (C). 



And first let us suppose the Earth, with its existing atmosphere, to occupy the place of 

 Venus, with the inclination of her axis of rotation to the plane of her orbit the same as at 

 present. Then should we have 



hQ = 67°,2 (C) at the equator, 



and = 28° pole; 



and if we suppose the entire effect of solar heat on the superficial temperature of the planet 

 to be 2hQ, in the absence of all horizontal transference of heat, we should have the mean 

 temperature of the equator 



= - 39°,5 + 134°,4 



= 94°,9 (C) ; 



