If we compare the electric current with a current of water, we may express the case as follows:--Lightning and the electric spark are like splashes of water falling from a great height, and making a great deal of noise and disturbance. The electric machine gives a kind of current which may be compared to a brook running along a stony bed, and making a great deal of noise with but little water. The next great discovery in electricity was how to produce a steady current, which we may compare with the full, steady, and noiseless flow of a good water-tap. This discovery was made in a very roundabout way. Towards the end of the eighteenth century, it was found that certain curious fish called “torpedoes,” or cramp fish, were capable of giving their enemies a severe electric shock. When this was proved, men of science inclined to the idea that all movements of muscles are electric. One of them, who made experiments with frogs, ventured the guess that a kind of electric vapour moves through all muscles and nerves, and produces not only the movements of animals, but also their sensations. Great efforts were made to discover this electric vapour or “animal electricity.” It was, however, not till the year 1790 that the first actual observation of something like animal electricity was made by a professor in Bologna of the name of Galvani. We are told that his wife, being in poor health, was ordered to eat frogs’ legs, and that the professor experimented with a few of those; but in his own account there is nothing about his wife or about frogs’ legs considered as food. He simply relates how he placed the hind legs of a frog together with a piece of its backbone upon a table on which his electric machine stood, but without the conductor of the machine touching the frog. One of his assistants happened to touch the nerves of the legs with a knife, and he observed to his surprise that a kind of shudder seized the legs of the dead frog. Another assistant thought that this only took place when a spark was coming from the electric machine. Galvani says:--“Astonished at this new observation he drew my attention to it. Although I was engaged in some quite different work, I was inflamed by an incredible zeal and desire to examine it and bring to light the cause that was hidden in it. I, therefore, touched one or other of the nerves with a knife, and at the same moment one of the assistants drew a spark from the machine. The effect was always the same. In every case the muscles of the legs were violently contracted at the moment at which the spark burst, just as if the animal had been seized with a cramp.”