110 G. F. Becker — Kant as a Natural Philosopher. 



merit as he possessed in the matter is consequently confined to 

 the attempt to account for the greater frequency of relatively 

 dense matter among the inner planetary rings. Euler sup- 

 posed the densities to be proportional to the square roots of the 

 mean motions. If a is the mean distance, this is equivalent to 

 making the density proportional to 1/a 3 / 4 . Lagrange in 1782* 

 assumed the density to be proportional to 1/a. In this 

 hypothesis Lagrange was anticipated by Buffonf in 1769. 



Modern results do not indicate such simplicity. Since there 

 is compression in the inner portions of a planetary body, mean 

 density must be a function of mass. This is perhaps a suffi- 

 cient explanation of the fact that Earth has a higher average 

 density than Mercury, Venus and Mars. The planetary densi- 

 ties are divisible into two groups. Those planets just named 

 do not differ very greatly in this respect. The outer group 

 from Jupiter to Neptune are vastly less dense, but it is not 

 certain that the diameters of these bodies represent anything 

 except the exterior of their atmospheres. They are probably 

 still highly heated, and their average density is not very dif- 

 ferent from that of the sun. Now the sun is certainly vastly 

 hotter and more expanded than the outer planets, and it must 

 therefore be composed of material which would be denser 

 than the mass of Jupiter at the same temperature. It is con- 

 ceivable that this difference is due solely to the greater pres- 

 sure within the sun's mass. 



Kant's opinion (1755) that Jupiter is still fluid seems to be 

 the earliest expression of that view. Buffon in 1778 announced 

 his opinion that both Jupiter and Saturn are fluid.J 



The theory of base-levelling has been so generally accepted 

 by geologists and physical geographers throughout the century 

 that it is scarcely worth while to mention individuals, but some 

 of those who do not happen to be familiar with Kant may be 

 glad to read a few of his vigorous sentences on the subject. 

 "In respect to change of the earth's shape there remains to be 

 discussed a single cause which can be reckoned upon with cer- 

 tainty ; it consists in the fact that the rain and the streams con- 

 tinually attack the land and sluice it down from the highlands 

 to the lowlands, gradually making the elevations into plains and, 

 so far as in them lies, strive to rob the globe of its inequalities. 

 The action is certain and no matter of opinion. The land is 

 also subject to this action so long as there is material on the 



*Nouveaux Mem. Acad. Berlin, 1782, p. 158. 



f Oeuvres comp. Paris, 1827, vol. i, p. 215. 



\ Epoques de la Nature. Oeuvres completes de Buffon, Paris, 1827. vol. v, p. 

 84. Miss A. M. Clerke in her History of Astr. in the 19th Century, 2d edition, 

 errs as to the date of Kant's publication on this subject and assigus the priority 

 to Buffon. 



