PROGRESS IN ELECTRICITY 



to convey the electric virtue is supported by pack- 

 thread." 



Soon after this Gray and his host suspended a pack- 

 thread six hundred and sixty-six feet long on poles 

 across a field, these poles being slightly inclined so that 

 the thread could be suspended from the top by small 

 silk cords, thus securing the necessary insulation. This 

 pack-thread line, suspended upon poles along which 

 Gray was able to transmit the electricity, is very sug- 

 gestive of the modern telegraph, but the idea of sig- 

 nalling or making use of it for communicating in any 

 way seems not to have occurred to any one at that 

 time. Even the successors of Gray who constructed 

 lines some thousands of feet long made no attempt to 

 use them for anything but experimental purposes 

 simply to test the distances that the current could be 

 sent. Nevertheless, Gray should probably be credited 

 with the discovery of two of the most important proper- 

 ties of electricity that it can be conducted and in- 

 sulated, although, as we have seen, Gilbert and Von 

 Guericke had an inkling of both these properties. 



EXPERIMENTS OF CISTERNAY DUFAY 



So far England had produced the two foremost 

 workers in electricity. It was now France's turn to 

 take a hand, and, through the efforts of Charles Fran- 

 C,ois de Cisternay Dufay, to advance the science of 

 electricity very materially. Dufay was a highly edu- 

 cated savant, who had been soldier and diplomat be- 

 times, but whose versatility and ability as a scientist 

 is shown by the fact that he was the only man who had 

 ever contributed to the annals of the academy inves- 



267 



