COMETS. 123 



doubtful to many minds when Napoleon led his legions from the West to perish amid the 

 i snows of Russia, and Moscow was in flames ! 



Science has been more recently occupied with two cometary bodies, insignificant in 

 their external aspect, but deeply interesting on account of the discovery that their orbital 

 course is included within the bounds of our system, and their predicted returns fulfilled 

 with unfailing punctuality. The first is known as the comet of Encke. It was observed 



in the year 1786, by Messier, traversing 

 the constellation Aquarius ; afterwards 

 seen by Miss Herschel, in 1795, in Cyg- 

 nus; and by M. Pons, in 1805, in Ursa 

 Major ; but no idea was entertained that 

 these were appearances of the same body, 

 till Encke, in 1819, established their 

 identity, in consequence of which the 

 comet has received his name. It passes 

 at its perihelion within the orbit of Mer- 

 cury, and has its aphelion midway be- 

 tween the paths of the telescopic planets 

 and Jupiter, its greatest distance from 

 the sun being twelve times its least dis- 

 tance, and its period of revolution 1203 

 days or 3-p () years. This object has now 

 seven times answered to the announcements made respecting its course, incontestably 

 establishing its character as a regular member of our system, moving in obedience to 

 its laws. The comet appears as a small globular patch of vapour, without any star- 

 like nucleus or tail, scarcely perceptible, and its dimness seems to be increasing. But 

 this insignificant and shadowy thing exhibits a deeply interesting and important phe- 

 nomenon, that of the gradual diminution of its periodic time, owing to a decrease in 

 the size of its orbit, the supposed effect of a resisting medium in space, which is urging it 

 nearer the sun, and may ultimately terminate its career as a separate body. The same 

 conclusion is entertained with reference to the planets, founded upon this peculiarity of 

 the comet of Encke. If the spaces in which they move is occupied by a resisting medium, 

 that, it is conceived, will, in the long run of ages, diminish their actual velocity, decrease 

 the centrifugal force, give more power to the solar attraction, draw them towards the 

 centre, and thus end the system. Such a speculation is, to say the least, premature. 

 We may admit the existence of an ethereal medium which shall perceptibly affect the 

 movements of a small vapoury globule, and offer no appreciable opposition to the solid 

 and weighty planetary masses. The proper course is to wait until such a medium is 

 placed beyond all doubt, for it cannot be said yet to be demonstrated ; and until we have 

 some evidence of its action in the case of the planets, before we reason upon it as a fact. 

 Besides the comet of Encke there is another whose periodicity has been ascertained, a 

 discovery due to M. Biela, in 1826. This is entirely a telescopic object, and without tail 

 or nucleus like the former. Its aphelion place is a little beyond the orbit of Jupiter, 

 its perihelion within that of Venus, its time of revolution 2461 days, or 6| years. This 

 was the comet which excited a large amount of apprehension for the safety of our 

 terrestrial mansion, prior to its return in 1832. It was calculated that a little before 

 midnight, on the 29th of October, it would cross the plane in which the earth revolves, 

 near the point where our globe itself would be on the morning of the 30th of November 

 following ; and, undoubtedly, had the comet been delayed a month by any disturbance, 

 a collision with its nebulosity would have taken place. The alarm was principally 



