| Examination of Kirkwood’s Analogy. 25 
bee ot AES, had been different from its actual value for any planet ; 
if the law of elasticity of particles for a given temperature and: 
distance ftom each other varied from one planet to another in the’ 
primitive or présent states; in either of these cases, the analogy of 
Kirkwood might have fa iled. Asit is, no such failure is noticed ; 
- > We are authorized, therefore, to conclude, that the Pres ayer 
~ tity of calorie,—the law of elasticity, —the quantity of mo 
ef rotation,—the past and present radii of percussion, ihe nae 
tive diameter of the generating surface of the rings, and the pres- 
_ ent dimensions and density of the planets, have been regulated 
by a general law, which has fulfilled for all of them the four fun- 
damental conditions of Kirkwood’s hypothesis. 
é é wa Mr. Walker had concluded, Mr. George P. Bond inquired 
x 
&> 
t. W. as to the applicability of his remarks on ‘abe rings 
to the case of the secondary ring in the system of Satur 
os Mr. W. replied, that in the case of the breaking up of a primary 
a ring, the day of the new planet would be equal to the year of * 
the ring, provided the new diameter was the same as that of the 
generating figure, and the same Jaw of decrease of density from 
centre to surface was preserved. In this case we should have 
K=rmv=r'mv' 
v=v 
and therefore p=p' 
Such, however, is not the case in fact with the primary plan- 
ets, The new diameter is sconivacied by the more immediate 
action of the central mass, more than it is expanded by the in- 
crease of free caloric. The ti new diameter is, therefore, so much 
_ Staller than the primitive D, that p’ is changed into p, and v’, or 
_ yearly mean angular velocity, is changed into v for the daily 
ue. 
Pe" 
4 
_ We may extend the nebular hypothesis, and Kirkwood’s anal- 
“ogy to the secondary systems. If they are laws of nature, they 
must apply to both. In the secondary systems the day and month 
are the same. his fact Hfas remained hitherto unexplained. 
Lagrange showed that if these values were once nearly equal, a hs 
libration sets in round a state of perfect equality ; but he offered 
NO conjecture as to the cause of the primitive equality. On the 
nebular and Kirkwood’s hypothesis, it would only be necessary 
that upon the breaking up of the ring, the primitive diameter of 
the generating figure and law of relative density of layers, should 
preserved, in artes to maintain aconstant valueof p=p’, and i. 
couseqnently of v= => 
Prof. gong has pi that the moon, and probably the other” 
