On lengthening the string still more, however, the extra weight proved too much for the strength of the silk suspending-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 supported 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 convinced 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 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 suggestive of the modern telegraph, but the idea of signalling 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 properties of electricity--that it can be conducted and insulated, 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 Francois de Cisternay Dufay, to advance the science of electricity very materially.

Dufay was a highly educated savant, who had been soldier and diplomat betimes, 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 investigations in every one of the six subjects admitted by that institution as worthy of recognition.
Dufay upheld his reputation in this new field of science, making many discoveries and correcting many mistakes of former observers.