TRANSACTIONS. 



No. I. 

 Of Comets. By Hugh Williamson, M. D., LL. D., SCc. SCc. 



[Read before the Society, 20th June, 1814.] 



The theory of comets, in all ages, has been very obscure. Those 

 bodies were formerly supposed to be portentous, and were deemed to 

 be temporary meteors. It seems, however, to have been generally 

 admitted, within the last two centuries, since telescopes have been 

 greatly improved, that comets are solid bodies, though of little use, 

 revolving round the sun, and suffering from him, at certain times, the 

 most astonishing degree of heat ; whence they have been called blazing 

 stars. In the year 1769, during the appearance of a remarkable comet, 

 I ventured an opinion on that subject, very different from the opinions 

 that had commonly been received. I presumed that comets do not 

 suffer a great degree of heat in any part of their revolution. That the 

 tail of a comet is not a flame of fire, but the atmosphere of the comet, 

 thrown behind the nucleus by the rays of light, in its approach towards 

 the sun, and illuminated by the refracted light of the sun. Hence I 

 inferred that comets, in all probability, like this earth, are globes inha- 



