3 i8 HISTORY OF SCIENCE. 



resorted to the expedient of hanging a ball by a piece of packthread 

 to the end of a short length of rod. 



He now tried to carry the electric virtue horizontally by supporting 

 his line of packthread by passing it through a loop of the same material 

 which hung down from a beam. In this case not the least sign of attrac- 

 tion was perceptible, and Gray concluded that the electric virtue must 

 have passed along the line until it arrived at the point where it was sus- 

 pended, when it must have gone up to the beam. Gray went the next 

 day to exhibit these experiments to his friend Wheler, and from the 

 parapet of his house to the ground, a distance of 30 feet, they found 

 that the line conveyed the electricity. Wheler then wished to see how 

 far the line would conduct it horizontally, and Gray described his non- 

 success of the preceding day. Wheler suggested that the packthread 

 might be supported on silk threads, as this material would have suf- 

 ficient strength with the smallest thickness, and be on that account 

 less liable to carry off the electrical virtue. The first experiment of 

 this kind was made on the 2nd July, 1729, in a long matted gallery, 

 the line of packthread being supported on cross lines of silk stretched 

 transversely on nails driven into the opposite walls. The line of pack- 

 thread was 80 feet long, yet the ivory ball at its extremity at once at- 

 tracted some light substances when the tube was rubbed. In order 

 still more to increase the length of line through which the electricity 

 might pass, the friends arranged the packthread so that, after passing 

 from end to end of the gallery, it should return, and the tube and the 

 ball being both at the same end of the gallery, care was taken that they 

 were yet sufficiently far apart to prevent any influence reaching the 

 ball except through the line, which was now 147 feet in length. The 

 result was as decided as before. The illustration opposite (Fig. 155) 

 represents Gray conducting these experiments, in which he is virtually 

 constituting for the first time an electric telegraph. In some subse- 

 quent experiments of the like kind, the silk supports broke under the 

 weight of the packthread. On this they attempted to hang their line 

 by some fine iron wire, because its thinness would, as they still thought, 

 prevent the electricity passing off. But the iron wire being too fine to 

 sustain the weight, some rather thicker brass wire was substituted. 

 And now, although the tube was well rubbed, not the slightest mani- 

 festation of electricity appeared at the ivory ball, and Gray concluded 

 that the wire carried off the electricity, recognizing now the fact that 

 it was not the smallness of the silk lines, but their nature, which caused 

 the former experiments to succeed. Gray found, soon afterwards, that 

 hair and some other substances have the same property as silk that 

 is to say, they do not allow the electricity to pass off through them. 

 He proceeded to institute a long series of experiments on various sub- 

 stances to ascertain their power of receiving electricity. For example, 

 he found that a soap-bubble may be electrified so as to attract thin 

 leaves of Dutch gold. Another experiment, which was thought to be 



