480 Transactions.— Miscellaneous. 
It is also worthy of note, that stars seen through comets have neither 
been displaced nor distorted, showing that the cometic matter has no refract- 
ing power. 
Another argument against the solidity of comets is, that two at least 
have been placed in the scales, and found to be practically imponderable— 
weighed in the balance, in fact, and found wanting. In 1770, Lexall's 
comet plunged through the system of Jupiter, passing between the planet 
and one of its moons. The comet was whirled into a new orbit, but the 
circular motion of Jupiter’s moons was not in the least degree interfered 
with. As if to make assurance upon this point doubly sure by an experi- 
ment with the smallest planet, as well as with the largest, Encke’s comet 
passed very near to Mercury some years ago, and was deflected from its 
course, affording a new and accurate measure of the mass of the planet. 
But Mercury himself was not in the least degree perturbed. This proves 
that the mass of a comet is quite insignificant. 
It may also be noted that in 1846 Biela’s comet divided into two, a 
greater and a lesser. These gradually parted from each other during 
thirteen years, in which period they made the circuit of their orbit twice. 
No perturbations were observed, to indicate that they sensibly attracted 
each other, and to give a clue to respective masses. With regard, then, to 
these three comets at least, the more general dictum of a philosopher of no 
low degree seems to be probable, ** that the solid matter of a comet might 
be put into a gentleman’s snuff-box.” 
If there be any resisting medium in the inter-planetary spaces, it is 
evident that vast, and almost imponderable bodies, like comets, would be 
the first to show in their motions the effects of it, just as a light object 
thrown through the air will show the resistance of the air far more clearly 
than a dense and heavy object.  Encke's comet is one of the several short- 
period comets now known. It was discovered in 1789, and has now made 
twenty-seven revolutions since its discovery. Each one has shown itself to 
occupy on the average about two hours and a half less than its predecessor, 
so that the comet now comes to its perihelion some five or six weeks earlier 
than it would have done according to the period it observed at the time of 
its discovery. ‘The fact that a number of eminent astronomers have attri- 
buted this effect to a resisting medium in space, is proof that no other 
sufficient cause is known to science. I am not aware that any other cause, 
with any degree of probability in it, has been assigned by any authority. 
Should it be proved that the comet is really describing a spiral course, 
the vortex of which is the sun, it will simply suggest to the mind how, in 
unimaginable years, the solid planet must sink into that vortex too. At 
the same time be it noted that, if a comet should ultimately prove to us 
