BLTC Press Titles


available for Kindle at Amazon.com


Vanity Fair

William Thackery


Theory of Colours

Johann Wolfgang von Goethe


The Diplomatic Background of the War

Charles Seymour


Leaves of Grass

Walt Whitman


Electricity, its nature, operation and importance in the phenomena of the universe

by William Leithead

Excerpt:

Although, as we have already seen, the means employed for the excitation of electricity are various, the effects are constantly the same. In every case of excitation one body robs the other of a portion of its electricity; the former becoming over-charged, and the other being minus its natural quantity. To the over-charged body the term of plus, or positive, has been applied; to the other, that of minus, or negative.

Experience has also taught us that similar phenomena are exhibited by a body in either of these states, viz. attraction and repulsion, with light, if the excitation is sufficiently energetic. If, for instance, we make use of a glass tube as our electric, and a piece of flannel to excite it, upon applying the glass tube to, or bringing it near to, the brass cap of the gold leaf electroscope, a divergence of the slips of gold leaf will take place. Then we apply the finger, to draw the electricity from the instrument, and the gold leaves resume their original parallel position^ Now let the flannel be applied, and the same effect will be produced as that which took place on the approach of the glass, viz. a divergence of the gold leaves. Now it might be inferred from this that, since similar causes produce like effects, both the excited bodies are similarly circumstanced as regards their electrical condition; but we shall soon see that this is not the fact. If we repeat the excitation, and first apply the glass tube, so as to cause divergence, and then apply the flannel, the gold leaves will again resume their parallel position. This experiment, as well as the following one, teaches us that the flannel and the glass exercise a neutralizing influence over each other; and that, to all appearance, there are two electric powers, similar in their action on the electroscope when separate, the neutralizing effect taking place either when they are acting together, or in opposition the one to the other. If, for instance, we once more repeat the excitation, and without separating the two bodies bring them near to the instrument, no effect will be produced; but the instant they are separated a divergence of the leaves takes place, as before.

Philosophers at first imagined that these phenomena were peculiar to the substances that were excited; and hence the power excited by rubbing glass was termed vitreous, and that resulting from sealing-wax, resinous electricity; but it is now demonstrated that both powers are called into activity in every case of excitation . and as their mutual counteraction of effect resembles an affirmative and a negative power, the terms positive and negative have been substituted for vitreotts and resinous. Indeed, what was called vitreous electricity may, under certain circumstances, be obtained from resinous bodies, and vice versa. Smooth glass, for instance, acquires vitreous or positive electricity by friction with every substance with which it has hitherto been tried, except the back of a cat, which becomes positive, leaving the glass in a negative state; but roughened glass, if rubbed with the same substances, becomes negative, while the rubbing bodies are rendered positive. Again, sealing-wax, which in general becomes negative, if previously scratched., so that the surface is rendered rough, exhibits signs of positive, or vitreous, electricity. Silk, with resin, is positive, or vitreous; but with polished glass, it is resinous, or negative. The following substances acquire vitreous, or positive, electricity, when rubbed with any of those which follow, in the order in which they are set down; and resinous, or negative, with any of those which precede :—

The back of a cat.

Polished glass.

Woollen cloth.

Feathers.

Wood.

Paper.

Silk.

Gum-lac.


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