Brilliant_ The Evolution of Artificial Light - Jane Brox [41]
In the late eighteenth century, in Italy, Alessandro Volta challenged Luigi Galvani's conclusion that convulsions in frogs, which Galvani had hung from brass hooks upon an iron trellis, were caused by innate electricity within the animals themselves. Volta argued that the convulsions were caused simply by the contact between the brass and the iron, and he proved his theory by creating the first modern battery, which he described in a letter to the Royal Society in London in 1800:
I obtain several dozen small round plates or disks of copper, brass, or better of silver, an inch in diameter, more or less; for example coins, and an equal number of plates of tin, or, what is still better, of zinc, of the same shape and size approximately.... I prepare besides a sufficiently great number of disks of cardboard, or cloth ... capable of imbibing and retaining considerable water.... I place, generally horizontally, on a table or other base, one of the metallic plates, for example, one of silver; on this first, I then place a second of zinc; on this second, I place a moistened disk; then another plate of silver, followed immediately by another of zinc, to which I can make succeed a moistened disk. I then continue ... always in the same direction.... I continue, I say, to form by many of these sets a column sufficiently high that it may be able to stand upright.
The charge would last for as long as the electrochemical interactions between the liquids and various metals lasted. Volta had created a sustained, continuous flow of electricity. As Park Benjamin, writing in the nineteenth century, noted, Volta's invention "made electricity manageable. He reduced the infinite rapidity of the lightning stroke to the comparatively slow but enormously powerful current, which in the future was destined to carry men's words from one end of the world to the other, and to produce the dazzling light inferior only to the solar ray."
Volta's "pile" immediately intrigued scientists across Europe and America, none more so than Sir Humphry Davy—creator of one of the first miners' safety lamps—who, at the beginning of the nineteenth century, held a post as chemist at the Royal Institution in London. Davy worked at refining Volta's pile and eventually had large batteries built in the basement of the institution's laboratory. He carried out a series of experiments with them, including demonstrations of the first electric lights. In 1802 he succeeded in making a platinum filament glow, if only momentarily, by infusing it with electric current. Then in 1809, with the aid of the largest battery yet—consisting of two thousand pairs of plates—he demonstrated the first lasting electric light, the voltaic arc. He passed a current through a charcoal stick, which served as a conductor of electricity; then he touched another charcoal stick to the first, and a spark jumped from the first to the second. As he pulled them apart, an arc of brilliant blue-white light leapt across the heated air between them. But light wasn't created by the arc alone; the carbons glowed incandescently.
Davy never took the voltaic arc beyond the demonstration stage—an enduring, practical electric light was still many decades away, for considerable problems had to be overcome. Not only did Davy's charcoal electrodes burn quickly and unevenly, but as the carbons burned down and the gap between them widened, the light sputtered, then failed. Scientists had to develop electrodes that would burn slowly and steadily,