A History of Science-2 [104]
in the same manner account for most of the other phenomena, and which seem inexplicable without attending to this principle. "Chance has thrown in my way another principle, more universal and remarkable than the preceding one, and which throws a new light on the subject of electricity. This principle is that there are two distinct electricities, very different from each other, one of which I call vitreous electricity and the other resinous electricity. The first is that of glass, rock-crystal, precious stones, hair of animals, wool, and many other bodies. The second is that of amber, copal, gumsack, silk thread, paper, and a number of other substances. The characteristic of these two electricities is that a body of the vitreous electricity, for example, repels all such as are of the same electricity, and on the contrary attracts all those of the resinous electricity; so that the tube, made electrical, will repel glass, crystal, hair of animals, etc., when rendered electric, and will attract silk thread, paper, etc., though rendered electrical likewise. Amber, on the contrary, will attract electric glass and other substances of the same class, and will repel gum-sack, copal, silk thread, etc. Two silk ribbons rendered electrical will repel each other; two woollen threads will do the like; but a woollen thread and a silken thread will mutually attract each other. This principle very naturally explains why the ends of threads of silk or wool recede from each other, in the form of pencil or broom, when they have acquired an electric quality. From this principle one may with the same ease deduce the explanation of a great number of other phenomena; and it is probable that this truth will lead us to the further discovery of many other things. "In order to know immediately to which of the two classes of electrics belongs any body whatsoever, one need only render electric a silk thread, which is known to be of the resinuous electricity, and see whether that body, rendered electrical, attracts or repels it. If it attracts it, it is certainly of the kind of electricity which I call VITREOUS; if, on the contrary, it repels it, it is of the same kind of electricity with the silk--that is, of the RESINOUS. I have likewise observed that communicated electricity retains the same properties; for if a ball of ivory or wood be set on a glass stand, and this ball be rendered electric by the tube, it will repel such substances as the tube repels; but if it be rendered electric by applying a cylinder of gum-sack near it, it will produce quite contrary effects--namely, precisely the same as gum-sack would produce. In order to succeed in these experiments, it is requisite that the two bodies which are put near each other, to find out the nature of their electricity, be rendered as electrical as possible, for if one of them was not at all or but weakly electrical, it would be attracted by the other, though it be of that sort that should naturally be repelled by it. But the experiment will always succeed perfectly well if both bodies are sufficiently electrical."[1] As we now know, Dufay was wrong in supposing that there were two different kinds of electricity, vitreous and resinous. A little later the matter was explained by calling one "positive" electricity and the other "negative," and it was believed that certain substances produced only the one kind peculiar to that particular substance. We shall see presently, however, that some twenty years later an English scientist dispelled this illusion by producing both positive (or vitreous) and negative (or resinous) electricity on the same tube of glass at the same time. After the death of Dufay his work was continued by his fellow-countryman Dr. Joseph Desaguliers, who was the first experimenter to electrify running water, and who was probably the first to suggest that clouds might be electrified bodies. But about, this time--that is, just before the middle of the eighteenth century--the field of greatest experimental activity was transferred to Germany, although both England and France were still