Day 5: The world's first battery, Musee d'histoire des sciences, Geneva

At the History of Science Museum on the shore of Lake Geneva, I was engrossed in the impressive collection of scientific apparatus and notes on the lives of the scientists who designed and used them. In one of the rooms, I stumbled on an account of one of the great blunders in the history of electromagnetism. We've all heard of Michael Faraday, but how many of us are familiar with Genevan scientist Jean-Daniel Colladon?

In 1825, Colladon was seeking to prove that a magnet presented to a coil of conducting wire can induce an electric current in the wire. In order to ensure that the magnet did not interfere with the galvanometer, he placed the latter in a different room. After presenting the magnet to the wire coil, he moved to the other room to observe the galvanometer, and saw that the needle had not moved. The young scientist had not realised that induction is transitory, and occurs only when the magnet passes in front of the wire. He would have observed this had he left the galvanometer in sight. Induction was eventually discovered by Michael Faraday in 1831.

Moving through the densely packed collection, in an unassuming glass case, I discovered one of the greatest inventions of all time... one of the original prototypes of Volta's first battery.

The physics question for today involves a bit of chemistry: How is this electric pile pictured above able to produce a voltage to push a continuous electric current around a circuit (the pile is made of alternate copper and zinc discs, separated by cardboard soaked in salt water)?