Lectures on electricity / by James Ferguson, F.R.S.

  • James Ferguson
Date:
1825
Catalogue details

Licence: Public Domain Mark

Credit: Lectures on electricity / by James Ferguson, F.R.S. Source: Wellcome Collection.

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    tor to the earth, as it is by any means driven into the conductor. But if the communication between the earth and the conducting body be cut off by means of any non-conductor, some of the electric fire may be forced into the conductor, by which means it will have more than its natural quantity; and the earth, from which that additional quantity comes, will have so much the less : which could never be, if the electric fluid were not of an elastic nature, or could not be compressed. 6. When any body has more than its natural quantity of this fire or fluid, it is said to be electrified positively, or plus ; and when it has less than its natural quantity, it is said to be electrified negatively, or minus. And bodies may be electrified either of these ways by the common machine.4 7. When bodies are electrified either of these ways, they repel each other; but if some be electrified plus, and others minus, they mutually attract: or, if one body be electrified plus, and the other no way at all,^ they also attract each other.6 Note 4. The above paragraph contains the outline of Franklin's hy- pothesis ; and it allows us to generalise and arrange our facts in this science in a more simple and intelligible way than could be effected by the hypothesis of Du Fay, which is usually adopted by the French electricians. Note 5. An amusing illustration of the nature of electrical cohesion, which may be considered as a modification of the above phenomena, is alluded to by Mr. Symmer. He had been accustomed to wear two silk stockings on the same leg, one of them white, the other black. When these stockings were drawn off together, nothing remarkable appeared ; but if, while they were both on, he rubbed his hands several times over them, and then drew off the outer or black one by itself, he heard a crackling noise, and in the dark perceived sparks of fire between them. When the stockings were separated, and held at a distance from each other, both of them appeared to be highly excited ; the white stocking positively, and the black negatively. While they were kept at a distance from each other, -both of them appeared inflated to such a degree, that they exhibited the entire shape of the leg. Two black or two white
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