. Carnegie Institution of Washington publication. gthe angle of incidence. Another somewhat better and thicker plate was nowinserted with the results shown in B. REVERSED AND NON-REVERSED SPECTRA. 17 TABLE 4. A. Same plate as in the preceding work,6 = cm. B. Thickness 6 = cm. No. offringes. i i (probablevalue) . No. offringes. i i (probablevalue). o1020304050 0° 0° 0° 4-4 5-8 7-37-4 9,59,6 1 1. 0° 9-5II. O o 10 2030 40 0° 0° 0° 7-3 7-09-5 0° 5-2 The second series here is practically the mean of t
. Carnegie Institution of Washington publication. gthe angle of incidence. Another somewhat better and thicker plate was nowinserted with the results shown in B. REVERSED AND NON-REVERSED SPECTRA. 17 TABLE 4. A. Same plate as in the preceding work,6 = cm. B. Thickness 6 = cm. No. offringes. i i (probablevalue) . No. offringes. i i (probablevalue). o1020304050 0° 0° 0° 4-4 5-8 7-37-4 9,59,6 1 1. 0° 9-5II. O o 10 2030 40 0° 0° 0° 7-3 7-09-5 0° 5-2 The second series here is practically the mean of thetwo, though the reason for these large discrepancies isnot clear to me, even in consideration of the wedge-shaped plates. The mean of the results may, however,be used for computation. The path-increment introduced by the glass of thick-ness 2 = cm. and index of refraction n = , atan angle of incidence i and refraction r for n fringes,beginning at i = o, may be written (see fig. 7, where I isthe incident ray) /cos (i —r)e\N. /i \ = en\ - — i) — \ cos r / cosr -0 This is a cumbersome equation. If the angles i are small, the cosines maybe expanded and then approximately which, since i = nr nearly, may be further simplified to Thus for the second set (mean) ° ° cm. The wave-length thus comes out very much too large, but in considerationof the inadequacy of the fiducial position, i = o°, this is not the probable values of i in the tables (computed from X correct) agreewith the third series. In addition to this the effect of slightly wedge-shapedplates, etc., can not be ignored. For the first set (mean values) the resultsare similar, being io5X = cm. if computed by the approximate equation. This is again too large, but theprobable value of i computed from the correct X, as before, agrees nearlywith the first series of this set. 18 THE INTERFEROMETRY OF 9. Continuation. Air column.—An air compensat
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