122 



SCENERY OF THE HEAVENS. 



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

 snows of Russia, and Moscow was in flames ! 



Science has been more recently occupied with comets of short periods, 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 byM.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^ - years. This object has now 

 frequently answered to the announce 

 ments made respecting its course, incontestably establishing its character as n regular 

 member of our system, moving in obedience to its laws. The comet appears as a small 

 globular patch of vapour, without any starlike nucleus or tail, scarcely perceptible, and 

 its dimness seems to be increasing. But this insignificant and shadowy thing exhibits a 

 deeply interesting and important phenomenon, 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 etherial medium 

 which shall perceptibly affect the movements of a small vapoury globule, yet 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 de 

 monstrated ; 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 object is also 

 without tail or nucleus, and scarcely visible to the naked eye. 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 



