Astronomical Notes. 279 



field-glass in the beginning of November, and seen with the 

 naked eye after being found. Comparatively few of the 

 comets discovered ever become visible to the naked eye. 



It is impossible to have our mind directed to this family 

 of ethereal bodies without the desire being awakened to know 

 more about them, to penetrate further into the hidden 

 mysteries concerning them which still remain unsolved. In 

 trying to do this we are under the obligation of considering 

 other men's work which appear in scientific publications, or 

 build up our theories on personal observation, or perhaps a 

 little of both. The enquiring mind naturally tries to solve 

 the problem of — What they are? From whence do they 

 come; and whither do they go? First we will notice their 

 specific gravity. We are told that they are the lightest 

 ponderable bodies known to exist in space. That they are 

 transparent is proved by the fact " that on November 9th, 

 1795, Sir Wm. Herschel " saw " the comet of that year pass 

 centrally over a small double star of the nth and 12th mag- 

 nitudes, and the fainter of the two components remained dis- 

 tinctly visible during the comet's transit over the star." — 

 From Gore's Astronomical Curiosities. Donati's Comet of 

 1858 (which I quite well remember) passed over Arcturus, at 

 a point near to the comet's neck, which was thousands of 

 miles in diameter, when the star shone through quite bright, 

 as if there had been nothing intervening, whereas this star 

 would be quite hidden by a moderately thin stratum of mist 

 or cloud passing over it. Those facts naturally lead to the 

 conclusion that they are of a gaseous nature. A perfectly 

 typical comet in its form is made up of nucleus, head, neck, 

 and tail. Quite a number of theories have been advanced to 

 account for the tail. On looking at a comet with a tail 

 approaching the sun, we would naturally suppose that the 

 tail was the effect of the lighter cometry matter being blown 

 behind the head by its great velocity through a resisting 

 medium ; but when we find that when it reaches perihelion 

 the tail is still turned away from the sun, and when receding 

 it precedes the head, when this is so we must try to find some 

 other way of solving the problem. It has been suggested 

 that the position of the tail, before, at, and after perihelion, 



