ELECTRICITY. 



concluded from this, that the electric virtue conferred on the tube by friction 

 passed spontaneously to the cork. 



It then occurred to him to inquire whether this transmission of electricity 

 would be made to other substances besides cork. With this view he obtained 

 a deal rod about four inches in length, to one end of which he attached an ivory 

 ball, and inserted the other in the cork, by which the glass tube was stopped. On 

 exciting the tube, he found that the ivory ball attracted and repelled the feather 

 even more vigorously than the cork. He then tried longer rods of deal ; next 

 rods of brass and iron wire, with like results. He then attached to one end 

 of the tube a piece of common packthread, and suspended from the lower end 

 of this thread the ivory ball and various other bodies, all of which he found 

 capable of acquiring the electric state when the tube was excited. Experi- 

 ments of this kind were made from the balconies of his house and other ele- 

 vated stations. 



With a true philosophic spirit, he now determined to inquire what circum- 

 stances attending the manner of experimenting produced any real effect upon 

 the results ; and, first, whether the position or direction of the rods, wires, or 

 cords, by which the electricity was transmitted from the excited tube, affected 

 the phenomena. For this purpose he extended a piece of packthread in a ho- 

 rizontal direction, supporting it at different points by other pieces of similar cord, 

 which were attached to nails driven into a wooden beam, and which were there- 

 fore in a vertical position. To one end of the horizontal cord he attached the 

 ivory ball, and to the other he tied the end of the glass tube. On exciting the 

 tube he found that no electricity was transmitted to the ball, a circumstance 

 which he rightly ascribed to its escape by the vertical cords, the nails support- 

 ing them and the wooden beam. 



Soon after this, Grey was engaged in repeating his experiments at the house 

 of Mr. Wheeler, who was afterward associated with him in these investiga- 

 tions, when that gentleman suggested that threads of silk should be used to 

 support the horizontal line of cord instead of pieces of packthread. It does 

 not appear that this suggestion of Wheeler proceeded from any knowledge or 

 suspicion of the electric properties of silk ; and still less does it appear that 

 Grey was acquainted with them ; for, in assenting to the proposition of Wheeler, 

 he observed, that " silk might do better than packthread on account of its small- 

 ness, as less of the virtue would probably pass off by it than by the thickness 

 of the hempen line which had been previously used." 



They accordingly extended a packthread through a distance of about eighty 

 feet in a horizontal direction, supporting it in that position by threads of silk. 

 To one end of this packthread they attached the ivory ball, and to the other 

 the glass tube. When the latter was excited, the ball immediately became 

 electric, as was manifested by its attraction upon metallic leaf held near it. 

 After this, they extended their experiments to lines of packthread still longer 

 when the silk threads used for its support were found to be too weak, and were 

 broken. Being under the erroneous impression that the escape of the elec- 

 tricity was prevented by the fineness of the silk, they now substituted for it 

 thin brass wire, which they expected, being still smaller than the silk, would 

 more effectually intercept the electricity ; and which, from its nature, would 

 have all the necessary strength. The experiment, however, completely failed. 

 No electricity was conveyed to the ivory ball, the whole having escaped by 

 the brass wire, notwithstanding its fineness. They now saw that the silk 

 threads intercepted the electricity, because they were silk, and not because 

 they were small. 



Having thus accidentally discovered the insulating property of silk, they 

 proceeded to investigate its generalization, and found that the same property 



