468 Dr. Boase on M. Faye's Memoir on the Existence of a 



more condensed in the vicinity of every celestial mass, and more 

 particularly around the sun, which in mass transcends all the 

 others. In calculating the amount of this density as progressively 

 increasing towards the centre of the system, the intense heat of 

 the sun need not be regarded as a modifying force ; for its rays 

 can in no way affect the aether, since it is perfectly diathermanous. 



The grand objection to the aether as a resisting medium ade- 

 quate to the explanation of cometai-y acceleration, is the state- 

 ment of M. Faye, that each comet would require a distinct zone 

 or ring in space, varying in density not regularly in the ratio of 

 the sun's distance, but sometimes inversely, as in the case of some 

 of Saturn's rings. Should this be established as a fact, some other 

 disturbing influences must be sought for besides aether as a re- 

 sisting medium ; but still this would not annul the existence of 

 aether, for it would ever remain a datum as a retarding influence 

 quantum valeat. 



In such a wide field for speculation, it is not difficult to ima- 

 gine that such rings may exist in space as cosmical or nebular 

 matter of extreme tenuity and yet really ponderous as compared 

 with the aether in which they are situated. Such matter may be 

 the residue of the solar zones, from which, according to Laplace's 

 theory, each planet was evolved; or, a new form assumed by 

 comets, which by the successive shortening of the major axis of 

 their orbits, have been reduced to their mean distance from the 

 sun, at which place the body is still very voluminous, and would 

 be still more rarefied if reduced to the state of a ring revolving 

 around the sun as in the case of Saturn. 



Before concluding, a few words may be said concerning the 

 operation of a repulsive force emanating from the sun, and which 

 is said to be sufficient for the explanation of all the phenomena 

 of comets, including the acceleration of the periodical comets : 

 yet in truth we know but little concerning these phenomena, 

 nothing concerning their rotation, although, as revolving bodies, 

 they doubtless do rotate. 



The radiant heat issuing from the incandescent surface of the 

 sun is certainly the vera causa of many calorific phenomena ; but 

 that it can accelerate directly or indirectly the motion of a comet 

 does not seem probable. A comet falling towards the sun with 

 enormously increasing velocity, like the return of a rocket to the 

 earth, will pari passu contract in volume, and consequently in- 

 crease in density, in consequence of the increased influence of 

 gravitation : when it has gained its perihelion, like a vibrating . 

 pendulum, it will be carried by its momentum from the sun with 

 gradually diminishing velocity and increasing volume until it 

 attains to its aphelion. If the comet, in its approach to the sun, 

 passes through a resisting medium, especially if revolving in a 



