Symmer's experiments are almost ludicrous. He wore two pairs of silk stockings, and found that white and black silk worn together became strongly electrified. When the two stockings worn on one foot were pulled off together, and then separated, they were found to be electrified, and attracted each other so strongly that a force of about one pound was required to separate them. The two charges, negative and positive, could, however, be separated. He thought, therefore, that there are "two electrical powers," not one, as Franklin believed. His belief was strengthened by examining a quire of paper through which an electric spark had passed, and finding that "the edges of the holes were bent two different ways, as if the hole had been made in the quire by drawing two threads in contrary directions through it." There was a long controversy regarding the two theories, and neither quite gained possession of the field. Each contained some truth, and each had its weak points. The two had more in common than men at that time thought. Galvani and the Electric Current Franklin had proven that there is electricity in the atmosphere, and that lightning is an electric discharge. A widespread interest in the electricity of the atmosphere followed this discovery. Aloisio Galvani, a physician in Bologna, Italy, in attempting to learn the effect of atmospheric electricity on the nerves and muscles of the human body, made a discovery which led to the electric battery and a knowledge of electric currents. Having dissected a frog, he laid it on a table on which stood an electrical machine. When one of his assistants touched lightly the nerve of the thigh with the point of a knife while a spark was drawn from the electrical machine, the muscles contracted violently, as if they were attacked by a cramp. When he held the knife by the bone handle, there was no convulsion as there was when he held it by the steel blade. He next thought it important to find out if lightning would excite contraction of the muscles. He stretched and insulated a long iron wire in the open air on the housetop and, as a storm drew near, hung on it a dissected frog. To the feet he fastened another long iron wire, which was allowed to dip in the water in the well. "The result," he said, "came about as we wished. As often as the lightning broke forth, the muscles were thrown into repeated violent convulsions, so that always, as the lightning lightened the sky, the muscle contractions and movements preceded the thunder and, as it were, announced its coming. It was best, however, when the lightning was strong, or the clouds from which it broke forth were near the place of the experiment."