144 Observations on the Tails of Halley^s Comet, 



of them may lead to the conclusion, that they are projected by local 

 causes from particular parts of the comet's nucleus, and revolving 

 with it, take at different times, different positions, a comparison of 

 which may determine the period of rotation. In the account of my 

 observations on Halley's comet, as well as in the following referen- 

 ces to its former appearances, the term tail will, unless otherwise 

 stated, be exclusively applied to the luminous train which was near- 

 ly opposite the sun. Whether in the accounts of its appearance 

 previous to 1835, its total length was given, or only that part seen 

 by direct vision, we may perhaps have no means of determining. 



The comet of 1305, believed to have been that of Halley, seems 

 to have presented an envelope and train, of such a magnitude as to 

 render it not only sublime, but, in that age, terrific. It was refer- 

 red to as the " cometa horrendse magnitudinis," in an age when rare 

 phenomena, instead of proving a stimulus to accurate observation, 

 excited either wonder or terror. In the year 1456, it presented a 

 tail 60° in length, and spread consternation throughout christian Eu- 

 rope. Its malign influences, in connexion with the Mahometan 

 conquests, were daily and publicly deprecated, a papal bull being 

 formally issued, and the church bells daily rung for that special pur- 

 pose. In 1682, its tail was reduced to one half, being 30° in 

 length. In the year 1705, Dr. Edmund Halley, having determined 

 its period to be about seventy five or seventy six years, (varying ac- 

 cording to the disturbing influence of the planets,) foretold its reap- 

 pearance in 1759. It appeared within a month of the time pre- 

 dicted ; and the fulfillment of this prediction, the first successful at- 

 tempt of the kind ever made by astronomers, has liberated the hu- 

 man mind from those superstitious terrors, which hairy or blazing 

 stars had always excited, and of which this comet in particular, had 

 been for so many times, and in such a peculiar degree, the innocent 

 cause. 



Its next return to its perihelion, was in November, 1835, but a 

 few days later in the month than was predicted. 



The fact that the difference between the actual and calculated 

 time, was much less than at the preceding return, evinces progress 

 in astronomy. My own humble observations, however, to which I 

 shall DOW proceed, have no bearing upon what, in the English use 

 of the term, is called physical astronomy. They relate rather to 

 the physics, and (if I may so express it) to the meteorology of com- 

 ets ; to points, which may interest the public and the natural phi- 

 losopher, but not the student of celestial mechanics. 



