g6 ON COMETS. 



though, as sometimes happens in matters of pure acci- 

 dent and in the run of chances, it is not very unfrequent 

 (and we have lately seen it remarkably exemplified) for 

 two or even three very great comets to follow each other 

 in rapid succession. Thus the great comet of 1680 was 

 followed in 1682 by two other very conspicuous ones, of 

 which we shall have more to say presently. 



(5.) When a comet is first discovered in a telescope it is 

 for the most part seen only as a small, faint, round, or oval 

 patch of foggy, or, as it is called, nebiilous light, somewhat 

 brighter in the middle. By degrees it grows larger and 

 brighter, and at the same time more oval, and at length 

 begins to throw out a " tail" that is to say a streak of light 

 extending always in a direction from the sun, or in the con- 

 tinuation of a line supposed to be drawn from the place of 

 the sun below the horizon to the head of the comet above 

 it. As time goes on, night after night the tail grows 

 longer and brighter, the "head" or nebulous mass from 

 which the tail seems to spring also increases, and within 

 it begins to be seen what is called a "nudetis" or kernel, 

 a sort of rounded, misty lump of light dying off rapidly 

 into a haziness called the " coma " or hair. Within this, 

 but often a good deal out of the centre, there is seen 

 with a good telescope and a high magnifying power a 

 very small spark or pellet of light which may or may not 

 be the solid body of the comet, and which is the real 

 nucleus. What in an indifferent telescope looks like a 

 rather large puffy ball, more or less oval, is certainly not 

 a solid substance. All the while the comet is getting 

 every evening nearer and nearer to the place of the sun. 



