Volta's battery

The story

The frogs' legs

In 1780 in Bologna a scientist and doctor, Luigi Galvani, was experimenting on frogs. One day he noticed that the legs of a dead frog, hanging from a copper hook, twitched as if it were alive when they were touched with an iron rod. Galvani thought he had discovered a new force, “animal electricity”: according to him, there was a special electric fluid in animals' muscles. In 1791 he published his results, and scholars all over Europe discussed them.

Among those who read Galvani's work was Alessandro Volta, a physicist from Como, born in 1745, who taught at the University of Pavia. Volta had already made important discoveries about electricity, but he did not agree about animal electricity. Repeating the experiments, he became convinced that the frog's legs moved not because of something in the animal, but because two different metals, in contact with a liquid, produced electricity. The frog was only a very sensitive detector. A great scientific dispute arose between Galvani and Volta.

How to make a current

To prove he was right, Volta wanted to produce electricity without animals. Until then scientists knew only “static” electricity, the kind that builds up when you rub, for example, a piece of amber or glass: you got sparks, but they lasted a moment and could not be used. Volta was looking for a way to get a steady flow of electricity.

In 1799, after years of attempts, Volta had the idea: he stacked a series of small metal discs, one of zinc and one of silver (or copper), alternating with pieces of cardboard or cloth soaked in salt water. One after another, all the layers formed a column: a “pile”. When he connected the two ends with a wire, he got a continuous electric current that did not run out at once. The more discs he added, the stronger the effect.

The letter of 20 March 1800

Volta described the discovery in a letter written in French, on 20 March 1800, to Sir Joseph Banks, president of the Royal Society, the most important British scientific academy. The invention was an enormous novelty: for the first time electricity could be produced continuously and under control. Within a few weeks scientists all over Europe had built piles and were trying them out.

As early as May 1800 two Englishmen, William Nicholson and Anthony Carlisle, used a pile to split water into hydrogen and oxygen, by “electrolysis”. In 1807 the English chemist Humphry Davy, with very large piles, managed for the first time to isolate new metals, such as sodium and potassium. In 1820 the Dane Hans Christian Ørsted discovered that a current makes a compass needle move, the first link between electricity and magnetism; and in 1831 Michael Faraday discovered how to produce a current with magnets, opening the way to generators and motors.

Volta was not a man who stayed shut in a laboratory: he travelled a great deal, to Paris, London and Germany, met the great scientists of the age and discussed with them. He was also a good teacher, able to explain with simple and spectacular experiments. That is why his discovery was understood at once and was immediately imitated.

Honours for Volta

Napoleon Bonaparte, who was interested in science, wanted to meet Volta. In 1801 he invited him to Paris: Volta showed his pile to the Institute of France, and Napoleon gave him honours and recognition. Later, in 1810, he made him a count. Volta went back to Como, where he lived quietly, and died in 1827. His name reminds scientists every day of his contribution: the unit of measurement of electric voltage is called the “volt”.

In Como, on the lake, there is a temple dedicated to him, the Tempio Voltiano (1928), which keeps his original instruments. His portrait was on the ten-thousand-lire banknotes until the end of the 1990s.