218 D. Kirkwood on Certain Analogies in the Solar System. 
4. These analogies seem to indicate, (1) the existence of a 
planet within the orbit of Mercury; (2) a similarity in the origi- 
nal constitution of the members of each pair; and (3)an intimate 
mutual dependence or connection in their primitive condition. 
5. If one trans-Neptunian planet should be hereafter discovered, 
the existence of a second would be rendered highly probable. — 
In the preceding article no special attention has been given to 
the objections of Professor Cherriman. Those, therefore, which 
have not been already discussed shall now be bfiefly con- 
sidered. 
Mr. C. first observes “ that this law is not universal, being in- 
applicable in the case of the outermost planet (Neptune, so far as 
we know), and also of the Sun regarded as the innermost planet ; 
in the former case, & being made to vanish by D becoming in- 
finitely great ; in the latter, by m vanishing.” If the planets 
were formed from rings of vapor, was the primitive breadth of the 
outermost. ring “infinitely great?” or does Neptune’s sphere © 
attraction extend beyond the fixed stars and the Milky Way? 
Will Professor Cherriman also inform us why the “analogy be- 
tween the periods of rotation of the primary pLanets,’” should be 
rejected because of its inapplicability to the Sun? (oe 
Mr. C. has calculated the values of the rotation, constant for 
Venus, the Earth, and Saturn. These values he thinks *‘ do not 
un. From this long since exploded hypothesis is derived the 
result which “compels” Mr. C. to withhold his assent from MY 
g 
. ‘ 
ae age ea a ae 
pai ey -s ud RUC Mat me 
ee. eae fh i) mt x 
* Professor 0,’s value of k for the Earth is grossly erroneous. 
