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The Tempest Prognosticator

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This incredible device - described as the 'Atmospheric Electromagnetic Telegraph, conducted by Animal Instinct' - was invented by Dr George Merryweather and unveiled to an unsuspecting public at the Great Exhibition at Crystal Palace, London, in 1851. Its design is a testament to man's ingenuity and deep desire to do things the hard way wherever possible.


The appropriately-named Dr Merryweather was well renowned as an inventor and, after inventing the 'platina lamp' (a device that burnt a mixture of ethanol and whisky) in 1830, became the honorary curator of the Whitby Literary and Philosophical Society's Museum. Through his work as a doctor, he became something of an expert on leeches and noticed they were particularly sensitive to electrical changes in the atmosphere. Wondering, with a stroke of genius, if leeches could be used in the developing science of meteorology, Merryweather spent most of 1850 experimenting with various designs and found that leeches could indeed be used to predict thunderstorms. After much discussion with the equally wonderfully named Henry Belcher, the president of Whitby Institute, Merryweather eventually came up with six designs of varying complexity and price.

On 27 February, 1851, Dr Merryweather read a three-hour essay describing his new invention to dignitaries at the museum, and the prototype Prognosticator was sent to London for the Great Exhibition.

How It Worked

The design was simple. 12 pint-sized bottles were arranged on a stand, each connected through a series of wires, chains and whalebones to a small hammer. The hammers in turn sat above a large bell.

After having arranged this mousetrap contrivance, into each bottle was poured rain water, to the height of an inch and a half; and a leech placed in every bottle, which was to be its future residence; and when influenced by the electromagnetic state of the atmosphere a number of leeches ascended into the tubes; in doing which they dislodged the whalebone and caused the bell to ring
- From Dr Merryweather's essay

Or, more simply, if a storm is coming the leech will react to the change in atmosphere and crawl up the bottle. When it gets to the top, a little Heath-Robinsonesque1 mechanism is triggered, resulting in a bell being struck. The individual bottle will then need resetting by dropping the leech back into the water and putting the hammer back into place.

Dr Merryweather didn't, however, consider leeches to be infallible. He called the arrangement of 12 of them his 'jury'; the more of them that rang the bell, the more likely it was that a storm would be on its way.

Did It Take Off?

Sadly, no, however amusing the idea of Met Office experts consulting their leeches may be2. Dr Merryweather lobbied the Government to have his device installed all around Britain's coastline, but failed. 'Storm Barometers', designed by Admiral Fitzroy3, were used instead.

What happened to the original device is unknown. However, 100 years later a copy was made for the Festival of Britain; this is now housed in Whitby Museum.

More recently, Philip Collins4 of Barometer World in Okehampton, Devon, has spent three years researching the design of the device. Indeed, he even familiarised himself with the behaviour of leeches by letting them feed from his arm. After 'many hundreds' of hours of work, a working model has been made, which is now on display at the attraction. Perhaps this man's dedication should be rewarded by a reproduction of his thoughts on leeches:

Leeches have an uncanny ability to sometimes predict the weather. They are unlikely to replace barometers despite their lower cost and small size, due perhaps to their unattractive appearance and a rather disturbing method of maintenance, although they do not hurt much. Barometers only cost money, not blood!
1William Heath Robinson was a British illustrator and artist, who was most famous for designing complicated machines. A good example of his style is 'The Building of the Saltash Bridge'.2Although maybe Michael Fish could have avoided his notorious incident - failing to predict 1987's 'Great Storm' - if he had used a Prognosticator.3He of the Beagle and Charles Darwin.4No, not that one.

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