# Page:Proceedings of the Royal Society of London Vol 59.djvu/180

166
[Dec. 12,
Indices of Refraction for the Electric Ray.

It will be observed that the ﬁnal results obtained from the two sets are freed from many of the unavoidable errors.

I give below the results of two sets of experiments each extending through eleven observations. The receiver was in an unusually good condition for nearly an hour, and during that time I took six observations with P to the front and six more with Q in the same position. As the receiver continued to remain in a fairly responsive condition I took five more for each set. As I have said already, greater weight should be given to the ﬁrst two sets of six readings, as being taken under the most favourable conditions.

In the ﬁrst two lines are given ten successive differences of the mean readings, taken with the cylinders P and Q.

 P .... 71 70 70·5 70·5 70·5 70 69·5 69·5 69·5 70 = 701 Q .... 70 70 71 71 70 71 71 70 70 69·5 = 703·5 Mean .... 702·25

${\displaystyle \scriptstyle {i={\frac {702\cdot 25}{2\times 10}}=35\cdot 11,\quad \mu =1\cdot 738}}$.

The following are the readings in degrees for the ﬁrst six sets of observations with P or Q.

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

Mean of A–B = 352·25.

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