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Machines of this sort have been made with plates 7 feet in diameter, and yielding sparks nearly 2 feet long. The properties of the "electric fire," as it was now called, were chiefly investigated by Dufay. To refine on the primitive experiment let us replace the shreds by a pithball hung from a support by a silk thread, as in figure 2.
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.
Von Guericke noted this, but failed to explain it satisfactorily. Dufay, repeating Von Guericke's experiments, found that if, while the excited tube or sulphur ball is driving the repelled feather before it, the ball be touched or rubbed anew, the feather comes to it again, and is repelled alternately, as, the hand touches the ball, or is withdrawn.
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.
It brought into harmony much fragmentary knowledge which had lain disjointed in the armoury of the physicist since Dufay in France and Franklin in America had investigated their theories of positive and negative frictional electricities, and had connected them with the flash of lightning as seen in Nature. Thus it became a fresh starting point both for industry and for science.
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. It has been shown in an earlier chapter how Von Guericke discovered that light substances like feathers, after being attracted to the sulphur-ball electric-machine, were repelled by it until they touched some object.
Dufay proved that there were two qualities of electricity, now called positive and negative, and that each kind repelled the like, but attracted the unlike.
It was so common that we are driven to something more substantial than a mere suspicion that Casella and Minuccio employed a similar method and that the domination of polyphonic thought in music had spread from the regions occupied by the church compositions of Dufay and his contemporaries downward into the secular fancies of people whose daily thought was influenced by the authority of the church.
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.
About 1733, as we have seen, Dufay had demonstrated that there were two apparently different kinds of electricity; one called VITREOUS because produced by rubbing glass, and the other RESINOUS because produced by rubbed resinous bodies.