( 246 ) 
3. For the measurements with methyl chloride of which the results 
are given below, the nicols were adjusted at an angle of 11 degrees 
from the crossed position. 
The dark band moved from one end of the spectrum to the other 
as the strength of the current varied from 20 to 60 amp. The 
observations were made with the electric are light and the calibration 
of the spectrum was obtained during the measurements by the 
brightest mereury lines, while the dispersion curve of the prism had 
been determined by means of sunlight. At each strength of the 
current three adjustments of the dark band were made and the 
means have been taken of the three pairs of readings of the galvano- 
meter and the cirele. Table 2 gives the galvanometer defections a 
so obtained, together with the wave-lengths 2 of the position of the 
dark band in the spectrum. 
Then on a subsequent day the testing tube was filled with water 
and the other parts of the apparatus remounted entirely unchanged. 
The dark band reappeared at strengths of the current deviating little 
from those found before, from which we could derive immediately 
that the rotation constants of liquid methyl chloride differed little 
from those of water. Thus the numbers of table 1 have been found, 
where « and 2 have the same meaning as they had before, and 7 
stands for the rotation constants in water. The latter have been 
derived from my measurements of communication n°. 73 '), and from 
them ar has been caleulated, which quantity must be constant for 
all values of 7, as it is equal to the rotation angle divided by the 
magnetic potential difference at the ends of the testing tube, and by 
the reduction factor of the galvanometer with its shunt. 
TABLE 1. 
| 
en iS r | ar 
! 
| 
el 
| 
935 | 588 ‘0.01307 | 3.071 
KOOI =o jeia | 3 062 
908.51 Dok 4487 3.100 
mean 3,078 
The mean value of ar, being 3.078, now served to derive the 
rotation constants @ of the methyl chloride from the a found. These 
2 . pe 1: EE m7 
values of @ have been plotted in a curve, from which ep = 001572 
1) Arch. Néerl. (2) 6 p. 825 (1901). 
