Page:Collected Physical Papers.djvu/61

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COLLECTED PHYSICAL PAPERS
41

In the next series of observations, the rays were refracted from air into glass. The electric beam was rendered parallel with the help of a glass lens (f = 4 cm.). The beam was incident on the plane face of the semi-cylinder. As the cylinder itself focussed the refracted beam, the objective hitherto used in conjunction with the receiver was dispensed with.

i. r. Mean value of r. μ.
40° 18°
19
18
18°   20′ 2·04
50° 22°
23
22°   30′
22° 30′ 2·00
65° 25°   30′
26°
27
26°   10′ 2·05

Mean value of μ = 2·03 ........ (4).

The different values of μ obtained are given below:—

From total reflection from a single semi-cylinder, 2·08 .... (1)
two semi-cylinders.. 2·04 .... (2)
From refraction from glass into air........ 2·04 .... (3).
air into glass........ 2·03 .... (4)

The frequency of vibration was of the order 1010.

The value of the index of the glass for sodium light by the total reflection method was found to be

μ = 1·53.

(Proc. Roy. Soc., Nov. 1897.)