The following experiments have satisfied me that M. Æpinus's account of the positive and negative states of the opposite sides of the heated tourmalin is well founded.
I heated the large stone in boiling water.
As soon as it was dry, I brought it near a very small cork ball, that was suspended by a silk thread.
The ball was attracted by one face of the stone, which I call A, and then repelled.
The ball in that state was also repelled by the positively charged wire of a phial, and attracted by the other side of the stone, B.
The stone being a-fresh heated, and the side B brought near the ball, it was first attracted, and presently after repelled by that side.
In this second state it was repelled by the negatively charged wire of a phial.
Therefore, if the principles now generally received, relating to positive and negative electricity, are true, the side A of the large stone, when the stone is heated in water, is in a positive state of electricity; and the side B, in a negative state.
The same experiments being made with the small stone stuck by one edge on the end of a small glass tube, with sealing-wax, the same effects are produced. The flat side of the small stone gives the signs of positive electricity; the high side gives the signs of negative electricity.
Again: