ROTATION OF LIGHT IN BISULPHIDE OF CARBON. 
355 
producing rotation in consequence of the properties of the CS 2 . It will be convenient 
to postpone the last correction, and take first the corrections for temperature in Pt 
and the E.M.F. of Clark, which relate rather to the machinery for measuring the 
current, and which can be made from data obtained in previous investigations. For 
this purpose 15° C. is adopted as the standard temperature; and the proportional 
corrections per degree are ‘00082 for the E.M.F. of Clark and ‘00044 for the R, 
making altogether ‘00126 per degree. For the observations of July 25, the correction 
is therefore 
+ 2‘6 X ‘00126 X 373 / -8= +2‘6 X ‘471 = + 1'*2. 
If we take as a standard current that which in traversing R at 15° would balance 
Clark I. at 15°, the double rotation of July 25 reduced so as to correspond with the 
standard current will be 
373 / ‘8+l'‘2=375 , ‘0. 
This rotation corresponds to the temperature 18°‘3 of the CS 2 . To obtain com¬ 
parable results we must reduce to a standard temperature, for which purpose we will 
select 18°. According to Bichat the rotation at t° may be expressed by 
1--00104* —‘000014* 3 , 
the rotation at 0° being taken as unity. To obtain a more convenient formula, 
applicable in the neighbourhood of 18°, we may write £=18+£'. Thus 
1 — ‘00104(5— ‘000014^= *9767 — ‘00154f'=‘9767(1 — ‘00158C); 
so that the coefficient for the correction is ‘00158. Hence, if the CS 2 on July 25 had 
been at 18°, we should have had 
375 , ‘0 + 375 / ‘0 X ‘00158 X ‘3 = 375 , ‘0+‘592 X ‘3 = 375-0+ ‘2 = 375 / ‘2. 
Thus reduced the results for the observations of different days should agree 
together. 
