Edison and the Electric Chair_ A Story of Light and Death - Mark Essig [4]
Electricity's ability to contract muscles also caught the attention of physiologists. A popular theory at the time held that the brain produced subtle "animal spirits" that were carried by the nerves to move the muscles of the body. Once it was found that electricity caused muscle contraction, some proposed that electrical fluid and animal spirits were one and the same—that electricity was the natural substance coursing through the nerves of animals.
In the 1780s the Bolognese physiologist Luigi Galvani was testing the effects of electricity on muscles. When he ran brass hooks through frog legs and hung them on an iron railing, he was surprised to see that the legs contracted spontaneously, without any application of the spark. He found that he could induce contractions by touching the frog leg in two places with different metals. Galvani supposed that the frog leg was a miniature Leyden jar, which he was discharging by the touch of two pieces of metal. Since there was no external source of electricity, the jolt must have come from within the frog leg—it was "animal electricity," he said, created and stored in muscle tissue.9
Galvani's results, published in 1791, did not convince everyone. Alessandro Volta, a professor of physics, claimed that the electricity that contracted Galvani's frog leg arose not within the leg itself but from the contact of brass hook and iron railing. This statement itself was controversial. All known electricity was created by rubbing glass or other insulators; Volta claimed that he could create electricity simply by bringing two different metals into contact. Volta convinced few people of this new theory of electrical generation until he created a device to demonstrate his point. He stacked multiple pairs of silver and zinc disks, placing a piece of wet cardboard between each pair. This electrical column, or pile, multiplied the effects of the individual pairs of disks and, when touched at either end, produced a palpable shock. Volta built a pile of forty pairs and gave himself a jolt through the ears: "The disagreeable sensation, and which I apprehended might be dangerous, of the shock in the brain, prevented me from repeating this experiment."10
The voltaic pile, created to quash the notion of animal electricity, had effects Volta never imagined. The pile could be used to charge Leyn den jars, which confirmed that this new electricity was similar to that produced by rubbing glass. But there were crucial differences. Previously, all electricity had been what is now called static—the buildup of a charge, followed by its transitory discharge. The pile created an electric current that flowed indefinitely and could be made stronger by adding more pairs of metal disks.
Volta's pile, described in a letter to London's Royal Society in 1800, set off a frenzy of experimentation. One man built a battery from two types of silverware, although it was more common to pair silver half crowns with zinc disks. By summer experimenters reported that when they attached two wires to a pile and ran the "galvanic current" through water, hydrogen bubbles formed on one electrode while oxygen formed a compound with the metal of the other electrode. The current, in other words, had decomposed water into its component parts, and the science of electrochemistry was born. Humphry Davy, a professor of chemistry at the Royal Institution in London, ran the current through two common substances—potash and soda—and produced tiny globules of previously unknown metals, which were named potassium and sodium.
Davy's prestige in London rested as much on his skills as a popular lecturer as on his scientific discoveries. Though important to science, electrochemistry offered little drama in the lecture hall,