Page:Popular Science Monthly Volume 8.djvu/625

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ized truths they are. The "Principles of Biology" is thus an attempt to explain the phenomena called vital, by general laws common to phenomena of every kind.

[To be continued.]




By Professor TYNDALL, F. R. S.

SECTION 1. Introduction.—Many centuries before Christ, it had been observed that yellow amber (elektron) when rubbed possessed the power of attracting light bodies. Thales, the founder of the Ionic philosophy (b. c. 580), imagined the amber to be endowed with a kind of life.

This is the germ out of which has grown the science of electricity, which takes its name from the substance in which this power of attraction was first observed.

It will be my aim, during six hours of these Christmas holidays, to make you, to some extent, acquainted with the history, facts, and principles, of this science, and to teach you how to work at it.

The science has two great divisions; the one called "Frictional Electricity," the other "Voltaic Electricity." For the present, our studies will be confined to the first, or older portion of the science, which is called "Frictional Electricity," because in it the electrical power is obtained from the rubbing of bodies together.

Sec. 2. Historic Notes.—The attraction of light bodies by rubbed amber was the sum of the world’s knowledge of electricity for more than 2,000 years. In 1600 Dr. Gilbert, physician to Queen Elizabeth, whose attention had been previously directed with great success to magnetism, vastly expanded the domain of electricity. He showed that not only amber, but various spars, gems, fossils, stones, glasses, and resins, exhibited when rubbed the same power as amber.

Robert Boyle (1675) proved that a suspended piece of rubbed amber, which attracted other bodies to itself, was in turn attracted by a body brought near it. He also observed the light of electricity, a diamond, with which he experimented, being found to emit light when rubbed in the dark.

Boyle imagined that the electrified body threw out an invisible, glutinous substance, which laid hold of light bodies, and, returning to the source from which it emanated, carried them along with it.

  1. A course of six lectures, with simple experiments in frictional electricity, before juvenile audiences during the Christmas holidays.