THE AID OF THE ACHROMATIC FRINGES. 



83 



the first result. Unfortunately, in neither case was the temperature of the 

 liquid taken ; for the temperature correction in case of these liquids is obvi- 

 ously very large. 



TABLE 6. Refraction of glass plate, e = 0.202 cm. thick, in liquid. Benzol, 8.5, /j. = 1.50381 

 (C), 1.50871 (D), 1.5163 (b), 1.52086 (F); dfjL/dt =0.0006. Aniline, 11.2, ^ = 1.58378 

 (C), I-59073 CD), 1.60882 (F); d/ji/dt = 0.0005, -B'=4-6Xio- n (glass). 



To endeavor to reconcile the low ju obtained in case of aniline with the high 

 values with benzol, experiments w r ere made at 16.5 C. The D line only could 

 be conveniently reached in the former case, whereas in case of benzol the dis- 

 placements were taken at the C, D, b, and F lines. The spectrum at C and F 

 was unfortunately too dark for sharp discriminations, but the results obtained 

 are given for all the cases in table 6. The displacement per 100 fringes was 

 at first taken at the D line only; later, when I found interpolation of doubtful 

 value, at the A and b lines also. These values are bracketed. From them the 

 coefficient X/Ajc follows. B was computed as above from Perkin's results and 

 B' (glass) temporarily put 4.6X io- n , there being no direct means of finding it. 

 The value of M at 16.5, corrected for the temperature of aniline and benzol, 

 still differs considerably in the two cases, i.e., as much as 0.0041. If the 

 above equations are correct and the rather large interpolation for temperature 

 differences (11.2 to 16.5 and 8.5 to 16.5) be admitted, then there remains 

 only the possibly insufficient purity of the distilled liquids, or the assumed 

 f? = 4.6Xio- u for glass, to account for this. 



The table gives Ax for benzol at the successive spectrum-lines visible. If 

 we suppose the displacement of wedge per 100 fringes does not vary in marked 

 degree with the color, we may compute (X/A#) and consequently 



B-B' = 



for intervals between the successive spectrum-lines. Here if X/Ax is replaced 

 by the mean value between two spectrum lines and considered constant and 

 if &c=(Az) c (A#) D , etc., 



