VOL. LXXVIII.] PHILOSOi'UICAL TRANSACTIONS. 353 



tricity. The instruments hitherto invented are still inadequate to the purpose, 

 and the known methods of operating are not free from considerable objections. 

 To examine the peculiar constructions, intended uses, properties, and defects, of 

 those instruments, as well as methods of performing the experiments, is the prin- 

 cipal object of the present lecture. The late Mr. John Canton first constructed 

 an electrometer, or instrument capable of showing the presence of what was then 

 considered as a small quantity of electricity. This instrument consisted of 2 small 

 balls of pith of elder or of cork, fastened to the 2 extremities of a linen thread, 

 the middle of which was fastened to an oblong wooden box, in which the thread 

 and balls were kept, when not actually in use. It was with such an instrument 

 that Mr. Canton himself. Father Beccaria, and others, ascertained the electricity 

 generally existing in the air; and that Mr. Ronayne discovered the constant elec- 

 tricity of fogs. But in the course of my experiments, having made frequent use 

 of such electrometers, it naturally occurred to me, that in several cases, when 

 the electrometer gave no signs of electricity, or at least not sufficient to ascertain 

 its quality, the cause of it was the relatively large size of the instrument ; for a 

 small quantity of electricity being diffiised through the box, thread, and balls of 

 the electrometer, had not power sufficient to separate the balls, and of course to 

 show its presence. In consequence of this, I contracted the size of the electro- 

 meters to such a degree as could be affected by less than the J 0th part of that quan- 

 tity of electricity which was necessary to affect Mr. Canton's electrometer. But 

 in making the electrometers very short, the stiffness of the threads, which had 

 been insignificant in a great extent, became now very considerable ; hence, in- 

 stead of fastening the balls to the 2 extremities of 1 piece of thread, I found it 

 necessary to suspend each ball by a separate piece of thread, the upper part of 

 which was formed into a loop, which moved in a ring of brass wire. 

 The electrometers, thus improved, were still subject to a great imperfection, 

 which was the twisting of the threads ; to avoid which I substituted fine silver 

 wire, instead of linen threads, which answered very well. However, in observing 

 the electricity of the atmosphere, these electrometers appeared to labour under a 

 considerable inconvenience, which was their being disturbed by the wind. To 

 remove this imperfection, I inclosed the electrometer in a bottle, which construc- 

 tion has been found to answer remarkably well. This bottle electrometer has 

 been since altered by various persons; though those alterations do not tend to im- 

 prove it altogether. M. de Saussure, by altering the shape of the bottle, and de- 

 priving it of a neck, has rendered it capable of retaining the communicated elec- 

 tricity only for a very short time ; whereas, some of those electrometers, con- 

 structed on my original plan, have retained the communicated electricity for more 

 than 4 hours. Besides other alterations for the worse. 



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