Ohm's Law Revisited

April 7, 2016 | 10:44
Ohm's Law by Ohm (photo by Lukas Mezger)
Ohm's Law by Ohm (photo by Lukas Mezger)
Who doesn’t know Ohm’s Law? I am not sure, but I think it is taught to (and immediately forgotten by) most children of around 14, 15 years old. Georg Simon Ohm, born in Germany in 1789, published his now famous findings in 1827. Some forty years later the unit of electrical resistance became the ohm and it stuck so well that we still use it today.

Cavendish, the man who weighed the earth

But did you know that James Clerk Maxwell – indeed, the same who proposed that electricity, light and magnetism might be related and came up with a set of partial differential equations to support his suggestion – published back in 1879 unknown work from Henry Cavendish, the man who weighed the earth, revealing that Cavendish had discovered Ohm’s Law more than 50 years before Ohm? Before Ohm was even born?

Since Cavendish didn’t publish his law, nobody knew about it and so the Royal Society committee that proposed the ohm as the unit for electrical resistance cannot be blamed for this grave injustice. Or can it?

Did Maxwell know?

Cavendish died in 1810, long before the publication of Ohm’s Law. He did not publish a lot, but he did write papers on his electrical experiments for the Royal Society. Maxwell, member of the Royal Society and of its units committee, had at some point come into possession of Cavendish’s papers that he published fifteen years after the ohm had come into existence.

Did Maxwell know of Cavendish’s work before the committee or did someone tip him off afterwards? We will never know. Is it important? Probably not. But, just for the sake of it, let me honour Cavendish once for his excellent but sadly forgotten work:

one volt applied to a resistor of one cavendish results in a current of one ampere flowing through the resistor.
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