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Nevertheless, Gray should probably be credited with the discovery of two of the most important properties of electricity that it can be conducted and insulated, although, as we have seen, Gilbert and Von Guericke had an inkling of both these properties. So far England had produced the two foremost workers in electricity.
"On making the experiment related by Otto von Guericke," he says, "which consists in making a ball of sulphur rendered electrical to repel a down feather, I perceived that the same effects were produced not only by the tube, but by all electric bodies whatsoever, and I discovered that which accounts for a great part of the irregularities and, if I may use the term, of the caprices that seem to accompany most of the experiments on electricity.
From the baptism of the first convert in 1707 and translation of the New Testament into Tamil, to the death in 1798 of Schwartz, with whom Carey sought to begin a correspondence then taken up by Guericke, the foundations were laid around Madras, in Tanjore, and in Tinnevelli of a native church which now includes nearly a million.
Boyle improved the pneumatic engine, invented by Otto Guericke, and was thereby enabled to make several new and curious experiments on the air, as well as on other bodies: his chemistry is much admired by those who are acquainted with that art: his hydrostatics contain a greater mixture of reasoning and invention with experiment than any other of his works; but his reasoning is still remote from that boldness and temerity which had led astray so many philosophers.
But, fortunately, one is rescued from this most un-German predicament by the porter of a waiting hotel omnibus, and so at last we have time to look about us, and to awaken to a realizing sense that we have reached the land of traditions; that we have come to Mecca; that we are in the quondam home of Guericke, Fichte, Goethe, Schiller, Oken, and Gagenbaur; in the present home of Haeckel.
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.
Von Guericke, however, recognized it as such, and refers to it as what he calls "expulsive virtue." "Even expulsive virtue is seen in this globe," he says, "for it not only attracts, but also REPELS again from itself little bodies of this sort, nor does it receive them until they have touched something else."
A common experiment to prove the weight of air is that of the Magdeburg Hemispheres, a simple contrivance of Otto Guericke, a merchant of that city. It is a part of every complete philosophical apparatus. It consists of brass caps, which, when joined together, fit tightly and become a globe. The air within being exhausted, it will be found difficult to separate them.
From this we may gather that Von Guericke himself did not realize the import of his discoveries, for otherwise he would certainly have carried his investigations still further. But as it was he turned his attention to other fields of research.
After the discovery of atmospheric pressure had led to the invention of the air-pump by Otto Guericke; and after it had become known that evaporation increases in rapidity as atmospheric pressure decreases; it became possible for Leslie, by evaporation in a vacuum, to produce the greatest cold known; and so to extend our knowledge of thermology by showing that there is no zero within reach of our researches.
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