Page:Collected Physical Papers.djvu/50

The following are the readings in degrees for the first six sets of observations with P (a, b) or Q (c. d).

P.
	a.		b.		Mean.		Difference.
1..........	216		144		188
							71
2..........	144		74		109
							70
3..........	74		4		39
							70	.5
4..........	(360	)+4	293		328	·5
							70	·5
5..........	293		223		258
							70	·5
6..........	223		152		187	·5
							352	·5	.... A.
Q.
	c.		d.		Mean.		Difference.
1..........	308		360	+18	343
							70
2..........	18		88		53
							70
3..........	88		158		123
							71
4..........	158		230		194
							71
5..........	230		300		265
							70
6..........	300		360	+10	335
							352	·0	.... B.

Mean of A–B = 352·25.

$\scriptstyle {i={\frac {352\cdot 25}{2\times 5}}=35\cdot 22,\quad \mu =1\cdot 734}$.

From the results given above it would appear that the index of refraction of sulphur is very near 1.734.

The method is also well suited for liquids; no large quantity of material is required; and the results possess a high degree of accuracy.

The determination of the indices of other solids and liquids are in progress. An account of these will be given in a future communication.

(Proc. Roy. Soc., Oct. 1895.)