Prof. Airy's New Optical Experiments. 14.1 



But it would be more accurate to solve the proposition by di- 

 rect analysis ; and writing this last equation as before, 



By reversing the series, we have 



h ~ A ^ A ^ A + ^ AT i ^ A^ ) 



Reviarlc. — The rule given in the Nautical Almanac is ac- 

 cording to equation [1], but upon the supposition that the 

 tables are not accurate beyond A'-«5 and consequently that 



A^M ought to be = 0, and therefore ^ is used in- 

 stead of A^M : thus 



u' = u + -J-AU + — -2F~^ ( ^ '); but now that 



the tables are sufficiently accurate it would be better to use 



A'm. 



And hence it seems to me that Mr. Baily has committed an 



oversight; for wishing to introduce A\ he has still employed 



/\^2i -4- A\ u 



', which was used only on the supposition that A^m 



ought to be neglected, and has written 



corrected in the Errata to 



^ k ^ 2h'' \ 2 )^ 6A» " 



instead of equation [1]. 



XVIII. Nena Optical Experiment by Professor Airy. 



[We are indebted to the kindness of a Cambridge friend for 

 the following account of some new optical experiments made 

 by Professor Airy : it announces some remarkable dis- 

 coveries, which have an important bearing in the verifica- 

 tion of the undulatory theory of light.] 



A N instructive variation of the experiment of Newton's co- 

 ■^^^ loured rings (suggested by the consideration of Fresnel's 

 formula- for the intensity of reflected vibrations) has lately 

 been made by Professor Airy. When a lens is placed on a 



plane 



