PROGRESS IN ELECTRICITY 



the explanation of this lay in the fact that ''when the 

 electric virtue came to the loop that was suspended on 

 the beam it went up the same to the beam," none of it 

 reaching the ball. As we shall see from what follows, 

 however, Gray had not as yet determined that certain 

 substances will conduct electricity while others will 

 not. But by a lucky accident he made the discovery 

 that silk, for example, was a poor conductor, and could 

 be turned to account in insulating the conducting- 

 cord. 



A certain Mr. Wheler had become much interested in 

 the old pensioner and his work, and, as a guest at the 

 Wheler house, Gray had been repeating some of his 

 former experiments with the fishing-rod, line, and ivory 

 ball. He had finally exhausted the heights from which 

 these experiments could be made by climbing to the 

 clock-tower and exciting bits of leaf -brass on the ground 

 below. 



"As we had no greater heights here," he says, "Mr. 

 Wheler was desirous to try whether we could not carry 

 the electric virtue horizontally. I then told him of 

 the attempt I had made with that design, but without 

 success, telling him the method and materials made 

 use of, as mentioned above. He then proposed a silk 

 line to support the line by which the electric virtue 

 was to pass. I told him it might do better upon ac- 

 count of its smallness; so that there would be less 

 virtue carried from the line of communication. 



"The first experiment was made in the matted 

 gallery, July 2, 1729, about ten in the morning. About 

 four feet from the end of the gallery there was a cross 

 line that was fixed by its ends to each side of the gallery 



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