and magnetic rotations. 
499 
Experiment 3. 
The apparatus was left many hours, in order that the 
electricity of its parts might, as far as possible, be dissipated. 
On returning to it, the glass disc was made to revolve with 
very great rapidity : not the slightest sensible effect was 
produced on the needle. 
Experiment 4. 
The needle was now electrified, and the same velocity 
being given to the glass plate, and all the other circumstances 
being the same, — the needle followed slowly. On trying 
various degrees of velocity, it was observed, that the effect 
on the needle was greatest when the motion of the glass 
plate was slow. A velocity of about five turns in a minute 
produced a considerable effect. 
Experiment 5. 
A stick of excited sealing-wax was substituted for the 
brass needle, and placed at the distance of about half an inch 
above the glass disc. On giving a slow motion to the glass 
plate, the wax needle followed in the same direction, and 
continued to move through many revolutions, notwithstanding 
the torsion of the silk ; but on giving the glass a very rapid 
rotation, the sealing-wax needle remained nearly immove- 
able. 
Experiment 6 . 
A new apparatus was constructed, which is represented 
in fig. 1 . It consisted of a circular piece of wood A B, g 
inches diameter, having a hole of 1.5 inches in the centre, 
