Updated: 15 June 2012 Beverley clock added Cox, Atmos updated

Gallery in course of arrangement

This gallery of the museum is dedicated to clocks with unusual motive power.

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CORNELIUS DREBBEL'S CLOCK: POWERED BY AIR PRESSURE CHANGES (?)
Cornelis Drebbel- the same man who is supposed to have rowed a boat underwater up the Thames- built a device in 1610 which was apparently a clock telling the time, date, and season. The gold machine was mounted in a globe on pillars and appears to have been powered by changes in air pressure. So far I have found no details of this.

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COX'S BAROMETRIC CLOCK: POWERED BY AIR PRESSURE CHANGES
In the 1760s the well-known clockmaker Mr James Cox developed a clock which was were wound up by changes in barometric pressure. The work was done in collaboration John Joseph Merlin, with whom Cox also worked on developing automata. Two large glass vessels containing no less than 68 kilograms (150 pounds) of mercury were connected together by an ingenious system of cords an pulleys so that the pulleys would rotate back and forth as the atmospheric pressure rose and fell. A sector-and-pinion mechanism converted this to unidirectional motion so that winding occurred on both rising and falling pressures. Cox claimed that his design was a true perpetual motion machine, which of course it was not.

Cox was a well-known clockmaker. He showed his self-winding clock in a private museum along with other fine clocks. When he died in 1788, a Mr Thomas Weeks bought the clock for his museum. It stayed in his museum until his death in 1833. It was not included in the sale catalogue of his effects in 1834, and remained lost until 1898 when it was exhibited at the Clerkenwell Institute. After a period on loan to the Laing Gallery in Newcastle, it was auctioned, and finally acquired by the V & A Museum in 1961.

Cox's clock is still in the Victoria & Albert Museum in London, but I do not know if it is on display; one of these days I mean to go and find out.

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THE BEVERLY CLOCK: POWERED BY TEMPERATURE AND AIR PRESSURE CHANGES
The Beverly Clock is displayed in the foyer of the Department of Physics at the University of Otago, Dunedin, New Zealand. It is powered by changes in air pressure, and more importantly temperature, acting on a 1 cubic-foot box of air which presses on a diaphragm and raises the clock weights, presumably by some sort of ratchet mechanism. The clock was built by Arthur Beverly in 1864. The clock has, like the Atmos described below, a torsional pendulum with a very slow period that requires very little power to keep it working; torsional pendulums are used in so-called "400-day" clocks. The Beverly Clock occasionally stops if the ambient temperature has not fluctuated enough.

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THERMO-PNEUMATIC CLOCKS: POWERED BY HEAT
The images in this section were very kindly provided by John Howell.

Left: The back of a Puja clock made by the German firm of Jauch and Schmid. The notion here is to power a clock reliably when faced with mains electricity of uncertain voltage and frequency. It is perhaps significant that the patent for the principle (No. 714893) was granted in Germany in 1940. At the lower left, shielded by a translucent housing, is a carbon rod resistance that heats the coloured alcohol in the glass vessel just above it. This causes some of the alcohol to vapourise, the pressure pushing the liquid up the connecting pipe to the vessel at top right. As the latter gets heavier the wheel bearing the four vessels experiences a torque that rewinds a remontoire* spring driving a conventional gear train and escapement. This clock has a pendulum-controlled escapement, but models with balance wheel escapements also existed. The firm of Jauch and Schmid was registered in 1930

*A remontoire, from the French 'remonter' (to rewind) is a spring or gravity reserve of power that can be configured to give a near-constant driving torque because it is rewound at frequent intervals from another power source- usually this was a mainspring, whose own torque would slowly decrease as it unwound. The idea was that rewinding a spring or lifting a weight at relatively frequent intervals isolated the escapement from the variable torque of the mainspring.

Left: Advertising material for the Puja clock movement. This version has a balance-wheel escapement attached instead of a pendulum.

To save you the trouble of grappling with a German-English dictionary, here are the translations of the salient words in the advert above; "wechselström" means "alternating current", "gleichström" means "direct current", "thermo-aufzug mit glaskolben-laufrad" translates as "thermo-lifter with glass bulb impeller", and "gehwerk" as "movement".

Left: Another Puja clock movement. It occurs to me that this arrangement must be very inefficient. It looks as though much of the heat would escape without doing anything useful. I also wonder if they were prone to catching fire.

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THE ATMOS CLOCK: POWERED BY TEMPERATURE AND AIR PRESSURE CHANGES

Anyone interested in oddly-powered clocks will have heard of the Atmos clock, which appears to be mostly powered by changes in temperature, and not, as its name might suggest, solely by changes in atmospheric pressure. A flexible metal capsule is filled with an inert gas and a little ethyl chloride, which vapourises as the temperature rises, causing the bellows to expand, and vice versa. A chain transfers this movement to wind the mainspring. A torsional pendulums with a long period is used to minimise the power required.

Left: An Atmos clock A temperature variation of only one degree in the range between 15 and 30 degrees Celsius, or a pressure variation of 3 mmHg, is said to be sufficient for two days' operation. I don't know if it is the case, but that seems to imply that the clock would stop working if the temperature fell below 15 degrees and stayed there, with the ethyl chloride remaining liquid. This is of course very possible in Winter. I also wonder how it copes with thermostatically-controlled central heating. The torsional pendulum makes only two oscillations per minute, which is 1/60th the rate of the standard seconds pendulum in a conventional clock. Because of the very slow movement of the gear train, no oil is used; it is claimed no measureable wear occurs.

Find out more:

http://www.compadapt.com/atmos.html

http://www.abbeyclock.com/lecoultre.html

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