PHYSICAL AND LITERARY. 5I 



And, after all, it Is no more than probable 

 €onjed:ure, that fuch an alternate accelera- 

 tion and retardation is brought about by the 

 influence of pulfes excited in the ethereal 

 medium : nay there are fome circumftances 

 in thefe phcenomena that feem hardly intelli- 

 gible by that hypothecs alone ; as, why the 

 intervals of the fits are lefs''^ in denfer 

 mediums ; and why they increafe fo faft and 

 in fo intricate a proportion, according to the 

 obliquity -{- of incidence. 

 . 48. According to Dr. Bradkys beautiful 

 theory of the aberration of light, the ftars 

 appear to be removed from their true places 

 to a certain diftance, by the proportion 

 which the velocity of the earth bears to the, 

 velocity of light : It is plain therefore, that, 

 on our hypothefis, a ftar muft have a diffe- 

 rent apparent place for every different colour; 

 that is, its apparent difk muft be extended 

 b3f the aberration into a longitudinal form 

 refembling the prifmatic fpedrum, having 



its 



friendly poles being alternately turned towards the furfaces 

 of bodies, they might be alternately difpofed to reflexion 

 and tranfmifiion ; and that at different intervals, in pro- 

 portion to the periods of their rotation. 

 * Nevji. Optics, b. 2. part 3. prop. 17. 

 -j- Prop. 15. ibidem. 



