. 
*. 
Wap 2 eee ee es 
‘ 
fere 
G. Hinrichs on Planetology. 
as the diffusion certainly is limited by the sinking of the denser 
particles. Ina nebula from which a whole cluster of solar sys- 
tems has been formed, we may therefore expect to find consider- 
ably different elements. We thus decline the imputation of 
Rutherfurd that homogeneity of original diffuse matter “is almost 
a logical necessity of the nebular hypothesis,” and cannot see 
any real vbjection to this hypothesis, if, as he says, “‘ we have now 
the strongest evidence that they (the stars) also differ in constit- 
uent materials” (this Journal, 1863, vol. xxxv, p. 77). 
In regard to the signification of 6 we must remark that, in the 
following, we use the letter 5 to represent the mean density of the 
nebula from the centre to the distance r, while in (17) 6 indicates 
the density of the sheil at the very distance 7. As (17) is only 
adduced to serve for a comparison, this course is legitimate. 
But it is easily demonstrated, that, at least for a spherical nebula, 
this law (1 7), if true for the individual shell, will also be true for 
the mean density of all shells inside of it. For, the actual den- 
sity varying according to (17), the mean density of the interior 
rom r=0 to r is found to be 
a) dan At EO ee kos A) 
where c’=4c, This law‘ is evidently the same as (17). 
§ 9. Attraction in the Nebula. 
mule (from Aféc. C6, liv. iii, ch. 1, § 4), independent of the law 
of the density (17), and merely depending on the proved uniform- 
ity of the density in each separate shell. 
we put 
3m A ] 19 
_— at ka a: . . * . s 
Q= 78 [tan ipa (19) 
then the components X, Y, Z, of the attraction (positive toward 
the origin) are 
zx 
os 
1 
x=Q. 
we 
y¥=9.%;- - - (20) 
a 
- 1 
as ) Zz (21) 
* The “ Density ” in Trowbridge’s article (this Journal, xxxviii, 354, 1864), is dif- 
nt, because referring to the density at different periods of time. 
