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KF5JRV > TECH 24.07.16 14:11l 71 Lines 4212 Bytes #999 (0) @ WW
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Subj: The Tempest Prognosticator
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The Tempest Prognosticator
The Tempest Prognosticator, also known as the leech barometer, is a
19th-century invention by George Merryweather in which leeches are used in a
barometer. The twelve leeches are kept in small bottles inside the device;
when they become agitated by an approaching storm they attempt to climb out
of the bottles and trigger a small hammer which strikes a bell. The
likelihood of a storm is indicated by the number of times the bell is struck.
Invention and development
Dr. Merryweather, honorary curator of the Whitby Literary and Philosophical
Society's Museum, detailed the sensitivity that medicinal leeches displayed in
reaction to electrical conditions in the atmosphere. He was inspired by two
lines from Edward Jenner's poem Signs of Rain: "The leech disturbed is newly
risen; Quite to the summit of his prison." Merryweather spent much of 1850
developing his ideas and came up with six designs for what he originally
referred to as "An Atmospheric Electromagnetic Telegraph, conducted by Animal
Instinct." These ranged from a cheap version, which he envisaged would be used
by the government and the shipping industries, to a more expensive design. The
expensive design, which took inspiration from the architecture of Indian
temples, was made by local craftsmen and shown in the 1851 Great Exhibition at
The Crystal Palace in London.
On 27 February 1851 he gave a nearly three-hour essay to members of the
Philosophical Society entitled "Essay explanatory of the Tempest
Prognosticator in the building of the Great Exhibition for the Works of
Industry of All Nations."
Method
The tempest prognosticator comprises twelve pint bottles in a circle around
and beneath a large bell. Atop the glasses are small metal tubes which contain
a piece of whalebone and a wire connecting them to small hammers positioned to
strike the bell. In his essay Merryweather described the workings of the device:
“ After having arranged this mouse trap 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.
The leech would have difficulty entering the metal tubes but would endeavour
to do so if sufficiently motivated by the likelihood of bad weather. By
ringing the bell it would signify that that individual leech is indicating
that a storm is approaching. Merryweather referred to the leeches as his "jury
of philosophical councilors" and that the more of them that rang the bell
the more likely that a storm would occur.
In his essay Merryweather also noted other features of the design, including
the fact that the leeches were placed in glass bottles placed in a circle to
prevent them from feeling "the affliction of solitary confinement".
Accuracy and success
Merryweather spent all of 1850 testing the device, sending a letter to the
president of the Philosophical Society and the Whitby Institute,
Henry Belcher, to warn him of an impending storm. The results of 28 of these
predictions are kept in the library of Whitby Museum. Merryweather stated in
his essay the great success that he had had with the device.
Merryweather lobbied for the government to make use of his design around the
British coastline but they instead opted for Robert FitzRoy's storm glass.
Replicas
The original device has been lost, but at least three replicas have been made.
The hundredth anniversary of the invention brought renewed interest as a
replica was made for the 1951 Festival of Britain. This non-working version
was made from the description in a printed copy of Merryweather's essay and a
copperplate drawing of the original. The device was shown in the Dome of
Discovery and given to the Whitby Philosophical Society when the festival
ended. Plans and photographs of this replica were then used to create faithful
working models, one at Barometer World near Okehampton, Devon, and another at
the Great Dickens Christmas Fair in San Francisco.
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