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ADAMS : RAYLEIGH-ZEISS INTERFEROMETER 



The values of r' /N for the other wave-lengths, determined 

 similarly are shown in the second column of the table 2. 



These values of r'/N were used to caluclate the values of N^ 

 in the fourth column, Nx being the wave-lengths for various 

 numbers of fringes corresponding to r = 3000 (and hence to 

 r' = 2634). The next, column contains the values of A^^X, 

 which is equal to p^, the path difference (for 3000 divisions) 

 for the given wave-length, while the sixth and seventh columns 

 contain respectively the proportional variation of pj. (that is, 

 Ap/pj), and the change (n) of refractive index of the compen- 

 sator plate calculated from Ap/p^ by means of formula (9 a). 

 The values of An calculated in this way agree satisfactorily with 

 the direct measurements (shown in the last column) of the re- 

 fractive index of the plate for the various wave-lengths. 



2. The shift of the achromatic fringe in white light. This shift- 

 ing of the achromatic fringe relative to the original central 

 reference fringe is common to all compensation interferometers 

 when used with white light. We may best understand what 

 happens by supposing that the concentration of a solution in 

 C (figs. 1 and 2) is increased slowly and continuously from zero 

 onwards and that at the same time the original achromatic 

 band is kept central by appropriate movement of the com- 

 pensator. We would then in most cases observe, that the 

 original achromatic band gradually becomes colored at the edges, 

 while the adjacent bands to right and left become respectively 

 more and less strongly colored; with further increase of concen- 

 tration the central band becomes identical in appearance with 

 the band on the left, and at length the latter is achromatic while 



