RR 
Miscellanies. 191 
rapidly, gives the appearance of a hollow sphere. Indeed it would 
easy to exhibit two or more concentric rings, revolving different 
ways, and with different degrees of velocity. I believe this is the 
first instance of the rotation of a conductor, effected by reversing its 
tangential action. 
Fig lo | : Fig. 2. > 
a 
Dp) ne aaa 
= 
Fig. 2, represents the electro-dynamic cylinder of Ampere, mount- 
ed in the same manner as the ring, (fig. 1.) This helix* of wire 
(called by some the pure voltaic magnet) has its ends bent inward, 
passing through its axis and brought out at its center, to be soldered 
to the segments 5,6. The arrangement otherwise is similar to fig. 1. 
The mode hitherto of exhibiting the magnetic polarity of this cylin- 
der, has been to float it, with a battery, in a large basin of acid and 
* The helix is wound on a cylinder of hard wood, loaded with two buttons, one 
at each end, to give it weight. 
