214 D. Kirkwood on Certain Analogies in the Solar System. 
years I have had a growing belief that Mercury is not the near- 
est planet to the center of our system. ‘This conjecture was 
first suggested by the fact that the-ratio of the sun’s diameter to. 
Mercury’s distance is much greater than that of the diameter of 
the arrangement of the planetary masses. This will be referred 
to hereafter. Upon the whole, I cannot but regard the probabili- 
ties as sufficiently strong to justify some search for the planet. 
Admitting its existence, an interesting question arises in regard to 
its perturbative influence on Encke’s comet. Perhaps the dim- 
inution in the period of the latter might in this way be at least 
partially accounted for. ok 
J? 
Application to the Asteroids.—If it be asked, what is the bear- 
ing of this analogy on the Olbersian hypothesis of the origin of 
the asteroids ?—I answer, it does not essentially require that those 
bodies should ever have been united in one perfect planet. It 
merely indicates what would have been the mass, mean dis-_ 
tance, and time of rotation of the resulting planet, had all the 
matter in the primitive ring collected about a single nucleus. If, 
however, we admit the hypothesis of an explosion, may we ne 
likewise suppose a subsequent disruption of some of the larger 
fragm In this case it might be impossible to trace all the 
resulting asteroids to the first point of separation. 
But it seems more probable that those small planets were form 
the separation of the primitive mass while in the nebular’ — 
other planets—chiefly that of Jupiter—either on the original ringy 
as suggested by Professor Peirce,* or on the asteroid-planet ; 
while in its primordial condition. In regard to the perturbations 
of this asteroid-ring, the following considerations may be worthy 
of notice : : 
1. Owing to the proximity of the asteroid-orbit to the enol 
mous mass of Jupiter, the disturbance would be very much great- 
er than in any other part of the planetary system. 
2. The breadth of the ring, or the primitive diameter of the 
planet, was probably such that the influence of Jupiter on opp 
site sides would be very unequal, 
* Gould’s Astronomical Journal, No. 27. 
