Abstract
By 1734, the French scientist Charles François de Cisternay du Fay had supposed that electrical phenomena may be attributed to the behavior of two distinct and invisible fluids: a vitreous electricity, produced by rubbing substances such as glass and gemstones; and resinous electricity, produced by rubbing substances such as amber and hard resin rods. According to Du Fay, each of these two fluids repelled the same, and attracted the opposite, kind of fluid. It is in this historical context that Franklin begins his famous Experiments and Observations on Electricity. As mentioned at the outset of his first letter to Mr. Collinson, Franklin has just received an “electrical tube” in the mail with which to carry out his very own experimental researches. By rubbing this glass tube with leather or silk and then drawing a knuckle along the tube, one could readily collect the “electrical fire” from the tube. When exploring the text below, try to put yourself in Franklin’s shoes, so to speak. That is: try to imagine that you yourself are approaching electricity for the first time. Is it conceivable that electricity is some kind of fluid? What experiments does Franklin perform? What conclusions does he draw? Does he adopt du Fay’s two-fluid theory of electricity, or something different? Is he correct? How do you know?
The electrical fire was not created by friction, but collected, being really an element diffused among, and attracted by other matter, particularly by water and metals.
—Benjamin Franklin
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Notes
- 1.
Much of the biographical information in this brief introduction is from Lemay, J. A. L., The Life of Benjamin Franklin, vol. 3, University of Pennsylvania Press, 2009. For a more “bawdy, scurrilous” depiction of his character, see Franklin’s satirical essays included in Franklin, B., Fart Proudly, Enthea Press, Columbus, Ohio, 1990.
- 2.
Thus, referring to electricity is like referring to ambricity, as was noted by Franklin himself.
- 3.
See Chap. 1 of the present volume.
- 4.
This power of points to throw off the electrical fire, was first communicated to me by my ingenious friend Mr Thomas Hopkinson; since deceased, whose virtue and integrity, in every station of life, public and private, will ever make his Memory dear to those who knew him, and knew how to value him.
- 5.
This was Mr Hopkinson’s Experiment, made with an expectation of drawing a more sharp and powerful spark from the point, as from a kind of focus, and he was surprised to find little or none.
- 6.
We suppose every particle of sand, moisture, or smoke, being first attracted and then repelled, carries off with it a portion of the electrical fire; but that the same still subsists in those particles, till they communicate it to something else, and that it is never really destroyed.—So when water is thrown on common fire, we do not imagine the element is thereby destroyed or annihilated, but only dispersed, each particle of water carrying off in vapour its portion of the fire, which it had attracted and attached to itself.
- 7.
This different Effect probably did not arise from any difference in the light, but rather from the particles separated from the candle, being first attracted and then repelled, carrying off the electric matter with them; and from the rarefying the air, between the glowing coal or red-hot iron, and the electrified shot, through which rarified air the electric fluid could more readily pass.
- 8.
These experiments with the wheels were made and communicated to me by my worthy and ingenious friend Mr Philip Syng; but we afterwards discovered that the motion of those wheels was not owing to any afflux or efflux of the electric fluid, but to various circumstances of attraction and repulsion. 1750.
- 9.
By taking a spark from the wire, the electricity within the bottle is diminished; the outside of the bottle then draws some from the person holding it, and leaves him in the negative state. Then when his hand or face is touch’d, an equal quantity is restored to him from the person touching.
- 10.
Our tubes are made here of green glass, 27 or 30 in. long, as big as can be grasped.
- 11.
This simple easily-made machine was a contrivance of Mr. Syng’s.
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Kuehn, K. (2016). Conservation of Electrical Charge. In: A Student's Guide Through the Great Physics Texts. Undergraduate Lecture Notes in Physics. Springer, Cham. https://doi.org/10.1007/978-3-319-21816-8_3
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