and magnetic rotations. 513 
below leno screen ; the lamp in the centre \ inch below the 
copper ; the sealing-wax needle -§■ inch above screen. I shall, 
in this instance, only give the gradual progress of the mean 
position of the needle, as calculated from the observations. 
Position of the mean point. 
O 
203 
203.5 
Lighted the lamp. 
200 
190.1 
189.9 
199-9 
205.3 
213-3 
212.0 
211.5 
217-3 
216.5 
221.3 
224.6 
This experiment presents the same results as the preceding 
one ; and shows, that the observed fact is not influenced by 
the eccentric position of the source of heat. 
As the silver wire, from which the needles were sus- 
v pended, had been unwound from a small cylinder, I thought 
it probable that it might be a little twisted ; in which case it 
would, from the weight of the needle, untwist until counter- 
balanced by the elasticity of the wire. If, in these circum- 
stances, heat were applied, it might happen that the elasticity 
of the wire would be altered, and consequently, from that 
circumstance alone, that the needle might change its position. 
If this were the case, on reversing the direction of rotation 
