BLTC Press Titles


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The Souls of Black Folk

W. E. B. DuBois


The Adventures of Sherlock Holmes

A. Conan Doyle


Darby O'Gill and the Little People

Hermenie Templeton Kavanagh


Some Experiences of an Irish R. M.

Edith Somerville and Martin Ross


Elements of electricity

by George John Singer

Excerpt:

At the commencement of the 18th century, the first Treatise on Electricity was published by Mr. Hauksbee: it contains an account of all the facts ascertained by his predecessors; and a variety of new experiments, made principally to ascertain the nature of electric light. His discoveries were numerous and important, but scarcely of sufficient magnitude to constitute a distinct epoch in the science. His most singular discovery was the great facility with which the electric light is produced in a vacuum.

Toward the year 1729, an important discovery was made by Mr. Stephen Grey, a pen* sioner of the Charter-house, who at that time cultivated this then infant science with great industry and address. Directing his attention to the nature of electric phenomena, he endeavoured to excite them in all known bodies, and by this means extended very considerably the catalogue of electrics; many substances in which no attractive power was excited by friction whilst in their natural state, became strongly attractive if rubbed after they had been moderately heated, but lost this faculty sooner or later when cooled. This fact clearly pointed out a relation between the state of bodies and

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their power of evincing electric appearances; and the nature of this relation was explained by Mr. Grey's subsequent experiments. Every attempt to render metals electric by friction had proved ineffectual in the hands of Mr. Grey, as well as in those of preceding inquirers, when it occurred to him, that as electric light appeared to pass between excited bodies and such as were incapable of excitation, the attractive power might be also capable of communication from one to the other. He inserted a wire and ball, by means of cork, in the extremity of a glass tube, and on rubbing the tube, found its attractive power was communicated to the wire and ball. He employed longer wires, till their vibration prevented him from extending them further. He then suspended the ball by means of pack-thread, from the tube; the electricity was still communicated. He ascended a balcony twenty-six feet high, and suspending tire ball from his tube by a proportional length of string, found that the electricity was communicated from the tube to it, so as to attract light bodies from the pavement of the court below. Associated with Mr. Wheeler, Mr. Grey afterwards extended his experiments, and in. one instance transmitted the attractive power of his excited tube through nearly 800 feet of packthread, without any apparent diminution of its force. In arranging the apparatus for these experiments, it was found that a silk line was incapable of transmitting the attractive power of the tube; an effect which these experimenters at first attributed to its comparative smallness; but they afterwards observed that a wire of much smaller diameter conveyed the electric effect completely, and thus discovered that there are in nature various bodies differently fitted for the transmission of electricity, some conveying it with facility to a great extent, and others apparently unsuited to transmit it to any perceptible distance. The first class of bodies are now called Conductors of Electricity,- and the second class Non-Conductors, or Electrics: terms which appear to have been first proposed by Dr. Desaguliers.

The experiments of Messrs. Grey and Wheeler show that conducting power does not depend on the magnitude, but on some pecu4iarity in the nature of "bodies; a peculiarity whose cause has not yet been discovered.

In 1732, M. Du Faye, Member of the Academy of Sciences at Paris, repeated and extended the experiments of Mr. Grey: he ascertained that the conducting power of packthread and other vegetable and animal substances is principally dependant on the water they contain: he conveyed electricity to greater distances by wetting the packthread, and found the conducting faculty became less perfect in most fibrous bodies in proportion as their natural moisture was expelled. He also observed, that such substances as were least susceptible of electric excitement by friction were the best conductors of electricity; though all the bodies he tried became electric by communication when placed on a non-conducting support. In this way he electrified himself, being supported by silk lines, and touched by an excited glass tube; and on this occasion the Abbe Nollet, who accompanied him in these experiments, drew the first electrical spark from the human body.

M. Pu Faye has also the merit of having given the first clear account of that apparent repulsion which obtains in most electric experiments, and was first observed by Otto Guericke, who had noticed that the fibres of an electrified feather receded from each other, and from the tube or globe with which they had been electrified. Du Faye viewed this phenomenon as the indication of a general principle in electricity, which may be thus expressed. Electrified bodies attract all those which are not so, but repel them as soon as they are electrified by their contact. Thus leaf gold is first attracted by an excited tube brought near to it, becomes electrical by the contact, and is then repelled; nor will it be again attracted while it retains its electric quality: but if it come in contact with any unelectrified body it loses its electricity, and will be again attracted by the excited tube; until, electrified by it, it is again repelled : and thus may alternate attraction and repulsion be produced as long as the excited tube retains its power.*


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