A History of Science
Tome I
Tome II
Tome III Tome IV

Book 2, chapter XIV
Progress in electricity from Gilbert 
and Von Guericke to Franklin
Experiments of Cisternay Dufay
So far England had produced the two foremost workers in electricity. It was now France's turn to take a hand, and, through the efforts of Charles Francois de Cisternay Dufay, to advance the science of electricity very materially. Dufay was a highly educated savant, who had been soldier and diplomat betimes, but whose versatility and ability as a scientist is shown by the fact that he was the only man who had ever contributed to the annals of the academy investigations in every one of the six subjects admitted by that institution as worthy of recognition. Dufay upheld his reputation in this new field of science, making many discoveries and correcting many mistakes of former observers. In this work also he proved himself a great diplomat by remaining on terms of intimate friendship with Dr. Gray - a thing that few people were able to do.

Almost his first step was to overthrow the belief that certain bodies are "electrics" and others "non-electrics" - that is, that some substances when rubbed show certain peculiarities in attracting pieces of paper and foil which others do not. Dufay proved that all bodies possess this quality in a certain degree.

"I have found that all bodies (metallic, soft, or fluid ones excepted)," he says, "may be made electric by first heating them more or less and then rubbing them on any sort of cloth. So that all kinds of stones, as well precious as common, all kinds of wood, and, in general, everything that I have made trial of, became electric by beating and rubbing, except such bodies as grow soft by beat, as the gums, which dissolve in water, glue, and such like substances. 'Tis also to be remarked that the hardest stones or marbles require more chafing or heating than others, and that the same rule obtains with regard to the woods; so that box, lignum vitae, and such others must be chafed almost to the degree of browning, whereas fir, lime-tree, and cork require but a moderate heat.

"Having read in one of Mr. Gray's letters that water may be made electrical by holding the excited glass tube near it (a dish of water being fixed to a stand and that set on a plate of glass, or on the brim of a drinking-glass, previously chafed, or otherwise warmed), I have found, upon trial, that the same thing happened to all bodies without exception, whether solid or fluid, and that for that purpose 'twas sufficient to set them on a glass stand slightly warmed, or only dried, and then by bringing the tube near them they immediately became electrical. I made this experiment with ice, with a lighted wood-coal, and with everything that came into my mind; and I constantly remarked that such bodies of themselves as were least electrical had the greatest degree of electricity communicated to them at the approval of the glass tube."

His next important discovery was that colors had nothing to do with the conduction of electricity. "Mr. Gray says, towards the end of one of his letters," he writes, "that bodies attract more or less according to their colors. This led me to make several very singular experiments. I took nine silk ribbons of equal size, one white, one black, and the other seven of the seven primitive colors, and having hung them all in order in the same line, and then bringing the tube near them, the black one was first attracted, the white one next, and others in order successively to the red one, which was attracted least, and the last of them all. I afterwards cut out nine square pieces of gauze of the same colors with the ribbons, and having put them one after another on a hoop of wood, with leaf-gold under them, the leaf-gold was attracted through all the colored pieces of gauze, but not through the white or black. This inclined me first to think that colors contribute much to electricity, but three experiments convinced me to the contrary. The first, that by warming the pieces of gauze neither the black nor white pieces obstructed the action of the electrical tube more than those of the other colors. In like manner, the ribbons being warmed, the black and white are not more strongly attracted than the rest. The second is, the gauzes and ribbons being wetted, the ribbons are all attracted equally, and all the pieces of gauze equally intercept the action of electric bodies. The third is, that the colors of a prism being thrown on a white gauze, there appear no differences of attraction. Whence it proceeds that this difference proceeds, not from the color, as a color, but from the substances that are employed in the dyeing. For when I colored ribbons by rubbing them with charcoal, carmine, and such other substances, the differences no longer proved the same."

In connection with his experiments with his thread suspended on glass poles, Dufay noted that a certain amount of the current is lost, being given off to the surrounding air. He recommended, therefore, that the cords experimented with be wrapped with some non-conductor - that it should be "insulated" ("isolee"), as he said, first making use of this term.





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© Serge Jodra, 2006. - Reproduction interdite.