What on earth?


‘Clockworks – main gallery – Bain far left


In a few days, Francoise Collanges will embark on a project involving the Alexander Bain clock at The Clockworks. We will survey the clock, compare it with examples at the Science Museum, the Guildhall and Greenwich, and work out how to operate it safely over the long-term.  Someone asked if we intend to drive it with an earth battery (the way Bain did), and this reminded me of an experiment, back in the 1990s.

Bain dial, signed


What’s an earth battery, you may ask? Remember the ‘potato clock’, where the power for a small battery clock comes instead from a galvanised nail and copper wire inserted into a potato? The potato provides the ‘electrolyte’ between the two metals – it’s the water in the potato really – allowing electrons to pass from the zinc to the copper, providing Volts. In an earth battery, the moist soil beneath the surface allows the same thing. The battery is ‘used up’ as the zinc disappears.

Carbon electrode


Elements can be ranked ‘galvanically’ – indicating the volts you can achieve from a combination. Magnesium/copper gives 1.45V, zinc/copper (potato clock) 0.9V. But Bain buried zinc plates and a lump of retort coke (carbon), producing 1.1V, enough for his sensitive clock.

Zinc electrode

In Leicester, an earth battery apparently powered a clock for about fifty years, and we set out to beat this run – calculating the zinc needed, given the rate at which it would be consumed – 2,671 grams in our case. Two specialist firms produced the carbon and zinc electrodes to our design.

What do you zinc of that, then? Zinc being buried.


I buried them a metre down and ran a clock for several months. But the battery stopped working. A post mortem suggests a flaw in our zinc block – it should probably have been a large thin plate – with maximum surface area. The thousands of surface flaws in Bain’s retort coke were actually an advantage. We could give it another go at The Clockworks – trouble is, we sit on concrete, so we’ll need to ask the neighbours if we can bury electrodes in their garden!


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2 Responses to What on earth?

  1. Peter Sweeney says:

    I recently (5 months ago) connected a Brille to an earth battery consisting of 6″ squares of magnesium and brass. The voltage has varied from 1.27 to 1.12v over a 6 month period but is at 1.26v this morning. The variation does not correlate with any weather pattern. The plates are 8″ apart set vertically and at a depth of just an inch below the surface. The set up was really to see if the Brille was a suitable candidate for such a battery. I am awaiting a long dry summer to see if the Brille will tell me when to water the garden!

  2. I owned this clock some time ago. It languished in the lower hallway of a medieval timber framed house on the only wall that was sound and straight enough to hang it well.

    It is an exceptional object and deserves the attention that I was unable to provide. It is good to see it in hands of people who want to see it working. All too often, clocks in museums are lifeless and dead. Under constant conditions, it can keep good time and was used for that purpose before it ceased domestic service.

    I do miss its distinctive clunk / tick sound.

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