Page:Collected Physical Papers.djvu/85

Rh is used, and the image is observed through a direct vision spectroscope, interference bands are observed in the spectrum, which flit across it with the slightest rotation of the cylinder.

I give below the results obtained from determinations made on different days (temp. = 26°).
 * (1) The larger apparatus was used for this experiment (diameter of the cylinder = 25 cm.), and the angle repeated fifteen times.
 * (2) Experiment with the smaller apparatus (diameter of the cylinder = 14·4 cm.). Reading was only taken of two successive positions for total reflection with the air-film 'direct' and 'reverse.'
 * (3) The same as above but with a different air-film.
 * (1) Angle repeated fifteen times.

Mean value for $$\scriptstyle{i=\frac{1459\cdot5}{2\times15}=48^\circ\ 39^\prime}$$

μ = 1·3321.

From (2) and (3), mean value of i obtained = 48° 40′.

The values of μ from the best determinations reduced to the temp. 26° are given below:—

The result obtained by me is thus seen to be practically the same as the above.

Having obtained the absolute value of the index of water for the D line and at the temperature of 26°, the G