But the greatest results came from the investigations of Benjamin Franklin, who proved that there was only one kind of electricity, that the two coatings of tin foil were both charged with it, that one had more than its ordinary quantity, while the other had less, and that the spark was caused by the transfer of electricity from one coating to the other. These discoveries were as much as any one discoverer might reasonably be expected to contribute; but Franklin soon followed them by his discovery of the power of points to collect and discharge electricity. He then pointed out with extraordinary clearness the fact that all the phenomena which had been produced by electricity were like those produced by lightning; and made the suggestion that lightning and electricity were identical. This was an interesting suggestion, but a suggestion only. To make it into a theory, or prove it as a law, an invention was required. Franklin made the invention. He conceived the idea of bringing down the electricity, with which he imagined that a storm-cloud was charged, by means of a long conductor, and of drawing off a spark from the lower end of the conductor as from an electrical machine. The long conductor he had in mind was a high spire that was about to be erected in Philadelphia. The erection of the spire being delayed, his imagination presented to his mind the picture of a kite flying near the cloud, and the charge flowing down the cord, made into a conductor by the accompanying rain. Forthwith, he embodied his conception in definite form by preparing a kite to which was connected a long cord, that ended with a piece of non-conducting silk, that was to be held in the hand, and kept dry if possible, and a key that was secured to the junction of the conducting cord and the non-conducting silk. The expectation was that the key would receive the charge from the cloud and give it out as a spark, if Franklin applied to it the knuckle of his disengaged hand. The invention was a perfect success in every way; sparks were given off, a Leyden jar was charged, and subsequent discharges of the Leyden jar were made to perform the same electrical feats as jars charged from ordinary electrical machines. (June, 1752.) The courage shown by Franklin in performing this experiment may here be pointed out. To the eye of a casual observer, he must have been trying to get struck by lightning.