COMETS. 



119 



invisibility and subsequent disappearance of this body, after once presenting itself, have 

 been sufficiently explained ; and a confirmation of the laws of universal attraction has 

 been drawn from circumstances apparently adverse to them. Its previous invisibility is 

 accounted for by its orbit being altogether different prior to the year 1770, its nearest 

 point to the sun being as distant as the path of Jupiter, corresponding, not to five, but to 

 fifty years of revolution. Its appearance that year arose out of the fact that in 1767 it was 

 in such close contact with the planet, moving in the same direction and in nearly the same 

 plane, that the attraction of the sun upon it was not ^y$ that of Jupiter. This entirely 

 altered the form of the orbit, and caused the comet to wheel its path towards that of the 

 earth, coming within our view, and executing the ellipse described by Lexel in the periodic 

 time of five and a half years. But why has not the comet since been seen ? Its passage 

 to the point of perihelion in 1776 took place by day ; and in 1779, before another return, 

 it again encountered the vast body of Jupiter, and suffered a fresh orbital derangement, 

 the attraction of the planet deflecting it into more distant regions. The comet therefore, 

 though " lost " to us, is in existence, and in each instance of its change of route has faithfully 

 obeyed the laws of gravitation. Those laws in 1770 introduced it as a bright and beau 

 tiful stranger to the notice of the human race, and again in 1779 stopped the fellowship, 

 removing the comet into a remoter path, where it is hid from the gaze of man, and 

 will be so unless some new perturbation directs its course towards the terrestrial orbit. 



Another comet, exhibiting some remarkable features, presented itself in the year 1807. 

 It was assiduously observed by Herschel in this country, and by the continental astrono 

 mers, Schroeter, Bessel, and Olbers. The drawings of the two former are here given, 



taken on two succeeding evenings, which show a divided tail, the separate branches 

 having varied their aspects. Coruscations, flickering and vanishing like the northern 

 lights, appeared to shoot out in an instant from the train to an immense extent. 



In the autumn of 1811, within the memory of many of the present generation, by far 

 the finest comet suddenly appeared to adorn our heavens, that had been seen since the 

 age of Newton. It was first beheld in this country in the beginning of September, and 

 was visible for more than three months in succession to the naked eye, shining with 

 great splendour, the observed of all observers. This was a comet of the first class in 

 point of magnitude and luminosity. Its brilliant tail, at its greatest elongation, had an 

 extent of 123 millions of miles, by a breadth of 15 millions ; and thus, supposing the 

 nucleus of the comet to have been placed on the sun, and the tail in the plane of the 

 orbits of the planets, it would have reached over those of Mercury, Venus, the Earth, 



