First, The under plate is excited, by rubbing its coated surface with a piece of new white flannel, or a fox’s tail. A hard shoe brush, having the bristles a little greased, will also excite sulphur very well. When this plate is excited as much as possible, it is placed on a table with the electric side uppermost; the metallic plate is then laid on the excited electric; then the metallic plate is touched with the finger, or with any other conducting substance, which receives a spark from it; finally the metallic plate being held by the extremity of its electric handle, is separated from the electric and after it is raised some distance, it is, on examination, found strongly electrified, with an electricity contrary to that of the electric, and will give a strong spark to a conductor brought near it. By placing the metallic plate upon the electric, touching it with the finger and separating them successively, a great number of sparks may be obtained, apparently of the same strength, and without exciting the electric again.—If these sparks be repeatedly given to the knob of a coated jar, it will become charged. The action of these plates depends upon the principle already laid down (page 22,) that an excited electric has the power of inducing a contrary electricity in a body brought within its sphere of action. The metal plate therefore, when set upon the excited electric, acquires a contrary electricity, by giving its electric fluid to the hand or other conductor which touches it, when the electric is positively electrified; or by acquiring an additional quantity from the hand &c. when the electric is negatively electrified. More fully to explain the principle here considered let the following easy experiment be made— Electrify any insulated conductor _positively_. Then if an electrometer[15] of cork balls be held at some distance from it, the balls will diverge with _negative_ electricity. This may be proved by bringing a piece of excited glass near them, as the balls will be attracted by it. But if you present to them a piece of excited sealing wax, they will immediately avoid it—that is, supposing the glass to be excited always positively, and the sealing wax always negatively.