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Ch. 10: Magnetic and Electric Tests

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CHAPTER X.
PHYSICAL PROPERTIES.
H—Magnetic and Electric Influences.
The word " electricity" is derived from the Greek " elektron," which was the name for amber, a mineralised resin of extinct pine-trees. It was well-known to the people of pro-historic times; later to the early Egyptians, and, at a still later date, we have recorded how Thales— the Greek philosopher, who lived about the close of the 7th Century B.C., and was one of the "seven wise men" —discovered the peculiar property which we call " elec­tricity " by rubbing dry silk on amber.
Many stones are capable of exhibiting the same phe­nomenon, not only by friction, as in Thales's experiment, but also under the influence of light, heat, magnetism, chemical action, pressure, etc., and of holding or retaining this induced or added power for a long or short period, according to conditions and environment.
If a small pith ball is suspended from a non-conduct­ing support, it forms a simple and ready means of testing the electricity in a stone. According to whether the ball is repelled or attracted, so is the electricity in the stone made evident, though the electroscope gives the better results. By either of these methods it will be found that some of the stones are more capable of giving and receiv-
Ch. 9: Heat tests on Gems Page of 118 Ch. 10: Magnetic and Electric Tests
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