ASTRONOMY. 



tude, as before, the aberration of the star in 

 right ascension is 



19".17 X cos (A L) 0".83 X cos (A + L) m 

 cosD 



and the aberration in declination is, 

 sin D(19 // .l7sin(A-L)-0 // .83sin(A+L)-8 // cosL XcosD). 



CAGNOLI, ibid. 

 DE LA MERE, ibid. 



From these four formulas, all the effects of aberra- 

 tion may be computed. Tables have been con- 

 structed for facilitating the calculations. VINCE, 

 Ast. vol. i. 513. & 522. 



The discovery of the aberration was made by Dr 

 BRADLEY, in 1725, from observation alone. He 

 has given an account of it, in a letter to Dr HAL- 

 LEY, Phil. Trans. N? 406. A very full extract of 

 this letter is in VINCE'S Astron. vol. i. $ 503. Af- 

 ter observation had satisfied him of the changes 

 above stated, in the latitudes of different stars ; he 

 discovered the cause to be the motion of light, 

 combined with the motion of the earth, as above 

 explained. 



. From the phenomena of the aberration, 

 the motion of the earth in its orbit is more di- 

 rectly proved than from any other fact in astro- 

 omy, 



Though 



