Page:On the Determination of the Index of Refraction of Glass for the the Electric Ray.djvu/7

Fig. 1.—The electric refractometer: P, the plate with a diaphragm; C, the semi-cylinder of glass; S, the shield (only one shown in the diagram); R, the receiver.

than the true reading and gradually increasing the angle till there was a response. The receiver was then placed at a greater angle, and the angle gradually reduced till the receiver again responded. In this way a series of readings for a particular angle of incidence was obtained. These readings were found fairly concordant, the maximum variation from the mean being not so great as 1°. One set of readings being taken on one half of the spectrometer circle, the cylinder was rotated in the opposite direction, and readings taken on the other side.

Angle of Incidence.		Angle of Refraction.			μ.
		Reading to the right.	Reading to the left.	Mean.
15°		31°   0′	31°   30′	31°   15′	2·00
		31   0	30   30
		31   30	31   30
		31   30	31   30
20°		45°   30′	45°   30′	45°   15′	2·08
		45   30	46   0
		44   30	44   0
		45   30	45   30
22°		48°   0′	49°   30′	49°   30′	2·03
		50   30	50   20
		49   30	48   30
		50   0	50   0

Mean value of μ = 2·04 ........ (3).