26 OBSERVATIONS OF SCHROETER. 



analogy, but from a series of telescopic observa- 

 tions continued for ten years on the surface of 

 Venus, by the celebrated Schroeter, who has 

 estimated the height of its principal mountains 

 as varying from 10*84 to 22-05 miles. So that 

 after making due allowance for the uncertainty 

 of such observations, it is probable that he has 

 arrived at an approximation to the truth. For, 

 as Venus is 1-40 times nearer to the sun than the 

 earth, and as the heating power of the sun is in- 

 versely as the squares of the distance, Venus 

 must receive more caloric than a given area of 

 the earth, in the ratio of 1*96, or nearly as 2 

 to 1, because the square of 1*40 is 1-96. For 

 the same reason, as the heating power of the sun 

 is 6*959 times greater at Mercury than on the 

 earth, which is 2*638 times farther from the sun, 

 the mountains of Mercury ought to be of corres- 

 ponding magnitude. And as Mars is 1*494 times 

 farther from the sun than the earth, he must re- 

 ceive 2*232 times less caloric ; which must pro- 

 portionally modify all the conditions of his sur- 

 face. In like manner, as Jupiter is 5-157 times 

 farther from the sun than the earth, he must 

 receive 26*594 times less caloric. And so on to 

 the extremity of the solar system. 



But in estimating the changes which the sur- 

 face of our planet has undergone during long 

 geological epochs, we must not overlook the in- 

 fluence of variations in the inclination of the 



