ROTATION OF LIGHT IN BISULPHIDE OF CARBON. 
359 
1-4542 
l-49 5 8 ==, 9^22 ampere =’09722 C.G.S. 
If the tube were infinitely long, the difference of magnetic potentials at its ends 
would be Amr ; but in the case of the actual tubes we have to introduce the 
correcting factors ’99433 and ’99353 (§ 15). Thus for the first tube, if x be the 
(single) rotation in minutes corresponding to difference of potential 1 C.G.S., the 
whole actual double rotation for a single passage of the light will be 
2 X ’09722 X 47m X'99433 X£C. 
From Series I. at 18° this quantity is found to be -g-X 1128’5, or 376’2, so that 
376-2 
x- 
2 x ’09722 x Ami x ’99433 
In like manner from Series II. we get 
-=’04203. 
x- 
375-7 
2 x ’09722 x 4 tto x ’99433 
’04198. 
For the second tube used in Series III. we have to employ a slightly different 
correction for finite length. We have 
375-8 
x= 
2 x -09722 x Ami x ’99353 
-=’04202. 
The results of Series I. and III. are thus in precise agreement, while that of 
Series II. is about toVo lower. Ascribing a somewhat less importance to Series II. 
in consequence of the smaller number of sets of observations, we may take as the 
final result of the investigation 
^='04202, 
which gives the rotation in minutes in bisulphide of carbon at 18°, corresponding to a 
difference of potential equal to 1 C.G.S. It should be noticed that the mean tempera¬ 
ture of the observations was so nearly 18° that the result as given depends scarcely 
at all upon Bichat’s formula for the dependence of the rotation upon temperature. 
22. M. Becquerel gives as his result for 0° C. ’0463 minute. To find the rotation 
at 18°, this must be multiplied by ’9767 according to Bichat’s formula: and as 
Becqtjerel’s observations were in fact made at about 18°, this reduction does not 
introduce, but rather removes, an extraneous element. Thus according to Becquerel— 
ce=’0452 minute, 
differing by about 7 per cent, from the value found by me. 
The comparison with Gordon is more uncertain, inasmuch as his observations were 
3 A. 2j 
