Ahhot and Fowle, Jr. — Aberration of Prisms. 25T 



For comparison with Lord Rajleigh's equation (19)|we derive 

 from equations (4), (3) and (6) 



,_FA_ 8^ cos(<^^ + S(^^) . . 



^^~^~cos(<^ + 8(^)"~cos(<^' + 8<^') ^ ^ 



BD = y'= ^^ + ^^^' ^ (u' + l)H' 



^ cos (</)'- 8<^') cos{cf>'-8cf>') ^' ^ 



y' u' A- I 



whence '—— — V (1-2 tan 6' . 8(i)' + . . . . ) (23) 



y u ^ 



That the approximations made in equations (19), (24) and 

 (25) of Lord Rayleigh's article may be of significance as mate- 

 rially affecting the value of Su, is shown by calculations made 

 with the following data : 



w = ]000'='", I = Q'5'''^ <^ = 50M2'20", _ . noa^ 



y = b'b'^ 8<j> = W3% «^'=30°0' 0", ^-^^'^^7 



Lord Rayleigh's formula gives : 



8v = 9-'7°'" 

 The formula deduced above gives : 

 8v=6-5'^'^ 



Astrophysical Observatory, Smithsonian Institution, June 15, 1896. 



