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ELECTRICITY. 105 



the science was not advanced by any capital discoveries. In that interval, 

 however, Otto Guericke, celebrated as the inventor of the air-pump, contrived 

 the first electrical machine. This apparatus consisted of a globe of sulphur, 

 mounted upon a horizontal axis, from which it received a motion of rotation, 

 by means of a common handle or winch. The operator turned this handle 

 with one hand, while with the other he applied a cloth to the globe, the friction 

 of whiih produced thi, electrical state. 



Aided by such apparatus, this philosopher discovered, that after a light sub- 

 stance has been attracted by and brought into contact with an electrified body, 

 it will not be again attracted, but, on the contrary, will be repelled by the same 

 body ; but that after it has been touched by the hand, its primitive condition is 

 restored, and it is again attracted. He also showed that a body becomes elec- 

 tric by being brought near to an electrified body without touching it ; but offer- 

 ed no explanation of this fact, which, as will be seen hereafter, indicated one 

 of the most important principles of electrical science. 



Whether it was that all his attention was altogether engrossed by the re- 

 searches which he prosecuted with such splendid results in astronomy, the 

 higher mechanics, and optics, or that facts had not yet accumulated in sufficient 

 number and variety to impress him with a just notion of the importance of elec- 

 tricity as a general physical agent, Newton bestowed on it no attention. One 

 experiment only proceeding from him is recorded, in which he shows that when 

 one surface of a plate of glass is electrified, the attraction will be transmitted 

 through the glass, and will be manifested by its effect on any light substances 

 placed on the other side of it. 



In the beginning of the eighteenth century, Hawkesbee made a series of 

 experiments on electrical light produced in rarefied air ; but as no consequences 

 were deduced from them affecting the progress of the science, we shall not 

 further iiotice them. In the construction of the apparatus for producing elec- 

 tricity, he substituted a glass sphere for the globe of sulphur proposed by Otto 

 Guericke. This was a considerable improvement ; and yet the experimental- 

 ists who followed abandoned it, and used no more convenient apparatus than 

 glass tubes, which were held in one hand, and rubbed with the other. To 

 this circumstance Dr. Priestley ascribes in a great degree, the slow progress 

 made by the immediate successors of Hawkesbee in electrical discoveries. 



About the year 1730 commenced that splendid series of discoveries which 

 has proceeded with accelerated speed to the present day, and now forms the 

 body of electrical science. Mr. Stephen Grey, a pensioner of the Charter 

 House, impelled by a passionate enthusiasm, engaged in a course of experi- 

 mental researches, in which were developed some general principles, which 

 produced important effects on subsequent investigations. 



The most considerable discovery of Mr. Grey was, that all material substan- 

 ces might be reduced, in reference to electrical phenomena, to two classes, 

 electrics and non-electrics ; the former, including all bodies then supposed to be 

 capable of electric excitation by friction ; and the other, those which were in- 

 capable of it. He also discovered that non-electrics were capable of acquiring 

 the electric state by contact with excited electrics. As the experiments 

 which led to these conclusions were of the highest interest, we shall hero 

 state them. 



Desiring to make some experiments with an excited glass tube, he procured 

 one about three feet and a half long, and an inch and a quarter in diameter. To 

 keep the interior free from dust, he stopped it at the ends with corks. When 

 this tube was excited, he happened to present one of the corks to a feather, 

 and was surprised to observe that the feather was first attracted, and then re- 

 \ polled by the cork, in the way it was wont to be by the glass tube itself. He 



