It was not until 1746 or 1747, after he had been making original researches in science for about five years, that he took up the subject of electricity, and he was then forty-one years old. It appears that Mr. Peter Collinson, of London, who was interested in botany and other sciences, and corresponded largely on such subjects, had presented to the Philadelphia Library one of the glass tubes which were used at that time for producing electricity by rubbing them with silk or skin. Franklin began experimenting with this tube, and seems to have been fascinated by the new subject. On March 28, 1747, he wrote to Mr. Collinson thanking him for the tube, and saying that they had observed with its aid some phenomena which they thought to be new.
"For my own part, I never was before engaged in any study that so totally engrossed my attention and my time as this has lately done; for what with making experiments when I can be alone, and repeating them to my friends and acquaintance, who from the novelty of the thing, come continually in crowds to see them, I have, during some months past, had little leisure for anything else."
It will be observed that he speaks of crowds coming to see the experiments, and this confirms what I have already shown of the strong interest in science which prevailed at that time in Pennsylvania, and which had evidently first aroused Franklin. In fact, a renewed interest in science had been recently stirred up all over the world, and people who had never before thought much of such things became investigators. Voltaire, who resembled Franklin in many ways, had turned aside from literature, and at forty-one, the same age at which Franklin began the study of electricity, had become a man of science, and for four years devoted himself to experiments.
Franklin was by no means alone in his studies. Besides the crowds who were interested from mere curiosity, there were three men--Ebenezer Kinnersley, Thomas Hopkinson, and Philip Syng--who experimented with him, and it was no mere amateurish work in which these men were engaged. Franklin was their spokesman and reported the results of his and their labor by means of letters to Mr. Peter Collinson. Within six months Hopkinson had observed the power of points to throw off electricity, or electrical fire, as he called it, and Franklin had discovered and described what is now known as positive and negative electricity. Within the same time Syng had invented an electrical machine, consisting of a sphere revolved on an axis with a handle, which was better adapted for producing the electrical spark than the tube-rubbing practised in Europe.