A HISTORY OF SCIENCE 



by two nails ; the middle part of the line was silk, the 

 rest at each end pack-thread; then the line to which 

 the ivory ball was hung and by which the electric virt- 

 ue was to be conveyed to it from the tube, being eighty 

 and one-half feet in length, was laid on the cross silk 

 line, so that the ball hung about nine feet below it. 

 Then the other end of the line was by a loop suspended 

 on the glass cane, and the leaf-brass held under the 

 ball on a piece of white paper; when, the tube being 

 rubbed, the ball attracted the leaf-brass, and kept it 

 suspended on it for some time." 



This experiment succeeded so well that the string 

 was lengthened until it was some two hundred and 

 ninety-three feet long; and still the attractive force 

 continued, apparently as strong as ever. On length- 

 ening the string still more, however, the extra weight 

 proved too much for the strength of the silk suspend- 

 ing- thread. " Upon this," says Gray, " having brought 

 with me both brass and iron wire, instead of the silk 

 we put up small iron wire; but this was too weak to 

 bear the weight of the line. We then took brass wire 

 of a somewhat larger size than that of iron. This sup- 

 ported our line of communication ; but though the tube 

 was well rubbed, yet there was not the least motion or 

 attraction given by the ball, neither with the great 

 tube, which we made use of when we found the small 

 solid cane to be ineffectual ; by which we were now con- 

 vinced that the success we had before depended upon 

 the lines that supported the line of communication 

 being silk, and not upon their being small, as before 

 trial I had imagined it might be; the same effect 

 happening here as it did when the line that is 



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