Page:Collected Physical Papers.djvu/61

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_ᴅ = 1·53.

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