BY G R. SMALLEY, ESQ. 333 



may have been the original path of a comet, that path might be 

 completely changed by the disturbing action of one or more 

 bodies within whose influence it happened to pass : and although 

 it must still continue to describe one of the conic sections, yet the 

 nature of the curve may be entirely altered in consequence of 

 the change of velocity produced by the disturbing planet. 

 Hence we are prepared to reconcile the apparent anomaly of the 

 parabolic or hyperbolic paths of comets, with our pre-conceived 

 notions of the superior and refined simplicity of the elliptic 

 orbit. We may fairly consider it by no means improbable that 

 comets were originally impressed with a motion which would 

 cause them to describe ellipses, and that the orbits they 

 subsequently moved in were the effects of perturbation, rather 

 than original design. 



Strangely enough, Jupiter and his Satellites seem continually 

 to have been " stopping the way " of comets. On two or three 

 occasions comets have threaded their way through Jupiter's 

 system, and whilst on the one hand none of the Satellites have 

 been in any degree affected, it has been plainly proved that the 

 comets have been considerably deflected from their previous 

 course. 



Without, however, troubling ourselves to enquire what may 

 have been the nature of a comet's path originally, it is sufficient 

 for our purpose to know that they are liable to be disturbed 

 when they come within the influence of our own system. 



It was such considerations as these that made the comet 

 which bears the name of Encke, so eminently his own. I have 

 already remarked that it was detected by Pons in 1819, but that 

 Encke proved its identity with one that had been observed on 

 three previous occasions. And this he did by calculating back- 

 wards the planetary perturbations to the respective times of 

 observation. With most indefatigable labour he successfully per- 

 formed this self-imposed task a work requiring high mathematical 

 genius extreme accuracy in computation sound judgment and 

 nice discrimination. The result was as he had anticipated ; he 

 found that the disturbing effects of the planets would have been 

 just such as to verify the correctness of the assumption, that the 

 comet which had been observed on the four occasions in question, 



