PHYSICAL AND LITERARY. 6x 



yond which it is invifible to a given eye j 

 for the denfities of the incident Hghts are 

 nearly as the fquares of the diftances of thefe 

 limits from the obje6t *. Does not all light 

 move with the fame velocity after reflexion 

 as before ; fince the angle of reflexion is al- 

 ways equal to the angle of incidence ? The 

 exception, made by fome, of eleftrical light 

 is founded on no lefs a miftake than con- 

 founding the luminous body with its light -f-. 

 But, the beft proof of this propofition is from 

 the coincidence of the computations of the 

 velocity of light, from the equation of the 

 eclipfes of Jupiter\ fatellites and the aber- 

 ration of the fixed flars J. 



QUER. 



* Let A and a (Tab. iii. fig, 6.) denote the fame or two 

 equal bodies of the fame colour illuminated with different 

 Rights, and B, b, the limits. As we fuppofe the light re- 

 ceived by the eye, at thefe points, is juft fufficient to affeft 

 it fenfibly and no more, the two lights at thefe different di- 

 ftances muft be nearly of the fame denfity ; taking therefore 

 in AB aline A/3 equal x.o ah, the denfity of the light at /5 muft 

 be, to the denfity of the light at^, nearly as AB^ to A^» ; 

 and, it is evident, that thefe denfities, at equal diftances, 

 muft be as the whole quantities of light refleded ; and thefe 

 again very nearly as the whole quantities of light incident. 



f MuJchenbroeckS Elementa Phyfices, late edition, in his 

 chapter on eleftricity. 



J Barnes's Tranfaft. vol, vi. &c, 



