308 Mr. J. S. Aldis on the Nebular Hypothesis. 



under a constant pressure c p ; and (2) that for aqueous vapour* 



a-\-t f p \ k ~ l 



as well as for the erases, the relation = ( — J * holds at two 



a + t \poJ 



points of the same unicursal curve, where the constant k has, of 



course, a different value from what it has in the case of gases. 



Zeuner holds, moreover, even a slight variation of the quantities 



c p and k to be not unlikely, wherefore the above equation would 



give the true relations approximately only. 



We may remark that the assumption of a constant c for va- 

 pours generally is not supported by Regnault's experiments* in 

 a conclusive manner; and for bisulphide of carbon it appears even 

 more decisively that a variation of c p must result from llegnault's 

 figures. 



I am engaged in a further prosecution of the observations 

 here communicated, and will report them hereafter. 



Bonn, February 2, 1869. 



XXXV. On the Nebular Hypothesis. 

 By J. S. ALDis,ilf .A., late Scholar of Trinity College, Cambridge^. 



THE test of theory is the deduction of numerical results. It 

 is not very easy to obtain such results from the nebular 

 hypothesis. Still the principle of the conservation of areas 

 affords a few results hitherto, we believe, unnoticed. They are 

 not, however, altogether free from objection. 



Every planet when detached from the central body, whether 

 as a ring or (as appears to us more probable) as the stalk end of 

 the pear-shaped central mass, must have rotated on its axis in 

 its periodic time round the central body. Assuming, then, 

 that the portions when detached did not differ much from a 

 sphere in shape, we calculate the densities of the different planets 

 when first detached. They are as follows, that of the earth being 

 unity : — 



Mercury .... -00113 



Venus -000241 



Earth and Moon . . -0000128 



Mars -0000411 



Jupiter -00000023 



Saturn -0000000285 



These results are strikingly in accordance with theory. Mer- 

 cury, Venus, and Mars have their densities nearly inversely as 

 the cubes of their distances, the others not. Whatever the law 



* Mem. de I' Acad. vol. xxvi. p. 163. 

 t Communicated bv the Author. 



