462 



the Earth, it must also be 368 times more feeble upon tJiauuS. 

 The relations of heat have not been mentioned here, because 

 they are complicated phenomena, dependent upon the exist- 

 ence or non-existence of an atmosphere surrounding the 

 planets, its constitution, and height. I will merely call to 

 mind here the conjecture of Sir John Herschel, as to the 

 temperature of the Moon's surface, " which must necessarily 

 be very much heated, possibly to a degree much exceeding 

 that of boiling water." 47 



b. SECONDARY PLANETS. 



The general comparative considerations trelating to the 

 secondary planets, have already been given with some com- 

 pleteness in the delineations of nature. (Cosmos, vol i. pp. 79- 

 83.) At that time (March, 1845,) there were only 11 prin- 

 cipal, and 18 secondary planets known. Of the asteroids, 

 so called telescopic, or small planets, only 4 were discovered : 

 Ceres, Pallas, Juno, and Vesta. At the present time (August, 

 1851,) the number of the principal planets exceeds that of 

 the satellites. We are acquainted with 22 of the former, 

 and 21 of the latter. After an intermission of thirty-eight 

 years in planetary discoveries (from 1807, to December, 

 1845), commenced a long series of 10 new small planets, 

 with Astrea, discovered by Hencke. Of these, 2 (Astrea and 

 Hebe) were first detected by Hencke at Driesen, 4 (Iris, 

 Flora, Victoria, and Irene) by Hind in London, 1 (Metis) by 

 Graham at Markree Castle, and 3 (Hygeia, Parthenope, and 

 Egeria) by De Gasparis at Naples. The discovery of the 

 outermost of all the large planets, Neptune, announced by 

 Leverrier, and found by Galle at Berlin, followed ten months 

 after Astrea. The discoveries now accumulate with such 



* Outlines, 432. 



