In September, 1752 [he wrote to Collinson], I erected an iron rod to draw the lightning down into my house, in order to make some experiments on it, with two bells to give notice when the rod should be electrify'd: a contrivance obvious to every electrician. I found the bells rang sometimes when there was no lightning or thunder, but only a dark cloud over the rod; that sometimes, after a flash of lightning, they would suddenly stop; and, at other times, when they had not rang before, they would, after a flash, suddenly begin to ring; that the electricity was sometimes very faint, so that, when a small spark was obtain'd, another could not be got for some time after; at other times the sparks would follow extremely quick, and once I had a continual stream from bell to bell, the size of a crow quill: Even during the same gust there were considerable variations. In the winter following I conceived an experiment, to try whether the clouds were electrify'd _positively_ or _negatively_. The result of these experiments, conducted with Franklin's usual painstaking completeness, was the conclusion on his part that thunder-clouds are, as a rule, in a negatively electrical state, and that, therefore, generally speaking, they do not discharge electricity upon the earth, but receive it from the earth. For the most part, he said, "_tis the earth that strikes into the clouds, and not the clouds that strike into the earth_." The thoroughness with which he addressed himself to the study of electricity was very marked. His investigation was as searching and minute as that of an anatomist engaged in the dissection of nervous tissue. Under his hands, the bare Leyden Jar became a teeming storehouse of instruction and amusement. He collected electricity from common objects by friction, he brought it down from the sky, he sought its properties in amber, in the tourmaline stone, in the body of the torpedo; he thought that he discerned it in the radiance of the Aurora Borealis. He put it through all its vagaries, juggled with it, teased it, cowed it until it confessed its kinship with the tempestuous heavens. He tested its destructive effects upon hens and turkeys, its therapeutic value to paralytic patients, its efficacy as a corrective of tough meat. He even, it is said, charged the railing under his windows with it to repel loafers standing about his front door. And, in his relations to electricity, as to everything else, his purposes were always those of practical utility. In one of his papers, he admits that he cannot tell why points possess the power of drawing off the electrical fire;