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The Fairy Tale of the Green Snake and the Beautiful Lily

Johann Wolfgang von Goethe, Thomas Carlyle, Rudolf Steiner


Paradoxes of the Highest Science

Eliphas Levi


The Picture of Dorian Gray

Oscar Wilde


Alice's Adventures in Wonderland

Lewis Carroll


History of the Inductive Sciences: XI. Electricity. XII. Magnetism. XIII. Galvanism, or Voltaic electricity. XIV. Chemistry. XV. Mineralogy. XVI. Systematic botany and zoology. XVII. Physiology and co

by William Whewell

Excerpt:

A little anterior to Dufay's experiments were those of Grey, who, in 1729, discovered the properties of conductors. He found that the attraction and repulsion which appear in electric bodies are exhibited also by other bodies in contact with the electric. In this manner he found that an ivory ball, connected with a glass tube by a stick, a wire, or a packthread, attracted and repelled a feather, as the glass itself would have done. He was then led to try to extend this communication to considerable distances, first by ascending to an upper window and hanging down his ball, and, afterwards, by carrying the string horizontally supported on loops. As his success was complete in the former case, he was perplexed by failure in the latter; but when he supported the string by loops of silk instead of hempen cords, he found it again become a conductor of electricity. This he ascribed at first to the smaller thickness of the silk, which did not carry off so much of the electric virtue; but from this explanation he was again driven, by finding that wires of brass still thinner than the silk destroyed the effect. Thus Grey perceived that the efficacy of the support depended on its being silk, and he soon found other substances which answered the same purpose. The difference, in fact, depended on the supporting substance being electric, and therefore not itself a conductor; for it soon appeared from such experiments, and especially2 from those made by Dufay, that substances might be divided into electrics per se, and non-electrics, or conductors. These terms were introduced by Desaguliers3, and gave a permanent currency to the results of the labours of Grey and others.

'Priestley's History of Electricity, p. 45, and the Memoirs quoted.

Another very important discovery belonging to this period is, that of the two kinds of electricity. This also was made by Dufay. "Chance," says he, "has thrown in my way another principle more universal and remarkable than the preceding one, and which casts a new light upon the subject of electricity. The principle is, that there are two distinct kinds of electricity, very different from one another; one of which I call vitreous, the other resinous, electricity. The first is that of glass, gems, hair, wool, &c.; the second is that of amber, gum lac, silk, &c. The characteristic of these two electricities is, that they repel themselves and attract each other." This discovery does not, however, appear to have drawn so much attention as it deserved. It was published in 1735; (in the Memoirs of the Academy for 1733;) and yet in 1747, Franklin and his friends at Philadelphia, who had been supplied with electrical apparatus and information by persons in England well acquainted with the then present state of the subject, imagined that they were making observations unknown to European science, when they were led to assert two conditions of bodies, which were in fact the opposite electricities of Dufay, though the American experimenters referred them to a single clement, of which electrized bodies might have either excess or defect. "Hence," Franklin says, "have arisen some new terms among us: we say B," who receives a spark from glass, "and bodies in like circumstances, is electrized positively, A," who communicates his electricity to glass, "negatively; or rather B is electrized plus, A minus." Dr. (afterwards Sir William) Watson had, about

3 Mem. Acad. Par. 1734. 3 Priestley, p. 66.

the same time, arrived at the same conclusions, which he expresses by saying that the electricity of A was more rare, and that of B more dense, than it naturally would have been4. But that which gave the main importance to this doctrine was its application to some remarkable experiments, of which we must now speak.

Electric action is accompanied, in many cases, by light and a crackling sound. Otto Guericke5 observes that his sulphur-globe, when rubbed in a dark place, gave faint flashes, such as take place when sugar is crushed. And shortly after, a light was observed at the surface of the mercury in the barometer, when shaken, which was explained at first by Bernoulli, on the then prevalent Cartesian principles; but, afterwards, more truly by Hawkesbee, as an electrical phenomenon. Wall, in 1708, found sparks produced by rubbing amber, and Hawkesbee observed the light and the snapping, as he calls it, under various modifications. But the electric spark from a living body, which, as "Priestley says\ "makes a principal part of the diversion of gentlemen and ladies who come to see experiments in electricity," was first observed by Dufay and the Abbe" Nollet. Nollet says7 he "shall never forget the surprize which the first electric spark ever drawn from the human body excited, both in M. Dufay and in himself." The drawing of a spark from the human body was practised in various forms, one of which was familiarly known as the "electrical kiss." Other exhibitions of electrical light were the electrical star, electrical rain, and the like.

'Priestley, p. 115.


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