366 ON THE MAGNETIC ROTATION OF LIGHT IN BISULPHIDE OF CARBON. 
of 4 amperes circulating about 1000 times round a column of bisulphide of carbon. 
With heavy glass, which is more convenient in ordinary use, the rotation is somewhat 
greater. With a coil of 100 windings we should obtain 15° with a current of 
40 amperes; and this rotation may easily be tripled by causing the light to traverse 
the column three times, or what is desirable with so strong a current, the thickness of 
the wire may be increased and the number of windings reduced. With the best 
optical arrangements the rotation can be determined to one or two minutes, but in an 
instrument intended for practical use such a degree of delicacy is not available. One 
difficulty arises from the depolarising properties of most specimens of heavy glass. 
Arrangements are in progress for a redetermination of the rotation in bisulphide of 
carbon.” * 
* From the Proceedings of the Cambridge Philosophical Society for Not. 26, 1883. See also ‘Nature,’ 
Dec. 13, 1883. 
