AEPINUS

Pyroelectricity

This stone has a property which distinguishes it from all others that are known at present, which is that when it is heated on hot coals it alternately attracts and repels the ashes which are around it. It does the same with metallic oxides, and in general with all other light bodies of whatever sort they are. The jewelers who put it in the fire to test its durability first noticed this property, and for this reason have given it the name of "the stone which attracts ashes." The authors whom I have cited also report this phenomenon but it has not hitherto been the object of any more particular investigations.

As soon as I heard of this remarkable peculiarity I conjectured at once that it owed its origin to electricity. I am under an obligation to our worthy colleague Mr. Lehmann, who first informed me of this property and who provided me with the means of making exact experiments on it. For this purpose he not only lent me a tourmaline stone which belonged to him, but procured for me also another one three times as heavy, which I acquired for myself. If I had not had this latter stone I should hardly have been in position clearly to recognize by way of experiments the astonishing properties of this stone, because it would have been very difficult, on account of the smallness of Mr. Lehmann’s stone, to discriminate exactly among the different phenomena.

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Laws of the Electricity of Tourmaline

I. Tourmaline always has at the same time both positive and negative electricity; that is to say, when one of its faces is positive, the other is without exception negative, and reciprocally.

This rule is easy to verify by experiment. For if we have examined the electricity which is on one of the faces of the stone it is only necessary to turn it around, when the other side will never fail to show distinctly the opposite electricity. But although this law is incontestably right the stone sometimes, as I shall show in the sequel, is in a sort of mean state in which the truth of this law cannot be clearly perceived.

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II. With a small pair of tweezers or in any other way immerse the tourmaline in boiling water or in some other hot fluid and draw it out after it has been there a few minutes. You will always find that in this experiment, however often you think it proper to repeat it, one face of the stone is positively electrified and the other negatively. The face of the stone which always comes out positive I shall call in the future the positive face and that which comes out in the other state the negative face.

We should specially notice that a strong electric state is produced in a body surrounded by water, which in all other eases seems to be the substance which is most harmful to the electric virtue. There is no real necessity to have the water actually boiling. A less degree of heat also excites the electricity of tourmaline but to a less extent. When the water is heated only to 108 or 110 degrees of Fahrenheit’s thermometer we can hardly discover any signs of electricity. The heat of boiling water seems to me to be in general that which renders the electricity of tourmaline most lively. If we heat this stone to a much higher degree on hot metal it shows only a feeble charge and does not become active until the stone has cooled down a little. The electricity that tourmaline acquires in boiling water still remains after the stone has entirely cooled down and I have even found it easily distinguishable in experiments made after six hours.