20 
ME. J. E. H. GOEDON ON THE DETEEMINATION OF 
Set 3. February 26. — 0 to 0.30 a.m. Same light. 6 cells. 
Plane of polarization. 
Scale-readings. 
Corrected deflections. 
No current. 
25-51 
Current direct. 
267 17 0 
267 26 0 
267 26 0 
6-40 
19-09 centims. 
267 19 0 
Mean 267 22 0 
Current reversed. 
280 57 0 
281 5 0 
280 59 . 0 
281 5 0 
Mean 281 1 30 
44-00 
18-48 centims. 
2R=13° 39' 30" a= 102-5 centims. 
#=18-785 centims. 
— = 8820'-6 y=-092907 
2E 
Tabulating the results, we have for — 
Set. 
2E 
2E 
y 
Cells. 
2. 
1 1° 58 30 
88611 minutes. 
5 
3. 
13 39 30 
8820-6 
6 
1 . 
15 26 0 
8917-5 
7 
See p. 32. 
To reduce the result to the D line, we may use one of the formulae given by M.Verdet * ; 
but as they are only approximate, I have thought it best to state the final result for the 
thallium line, wave-length 
(5*349)10“ 5 -f, 
on which the experiments were made. The wave length of the D line is 
(5-892)10- 5 f. 
Value ofVL. 
The ratio of H at Dorking to H at Kew was determined by vibrating the same magnet 
at the two places, and determining the times of vibration. We then know that the 
values are inversely as the squares of the times of vibration. 
Mr. Whipple, Director of the Magnetic Observatory at Kew, had the great kindness, 
* G3uvres, tom. i. p. 211. t Watts’ Index of Spectra. 
