The Polished Prognosticator of the Playful Physician

             … and if you think that’s weird, then what do you make of the Tempest Prognosticator? This fabulous contraption was invented by the aptly named Dr George Merryweather, who was inspired by a couple of lines from the poem Signs of Rain by Edward Jenner,

“The leech, disturb'd, is newly risen.

Quite to the summit of his prison.”

Edward Jenner - Signs of Rain

This couplet brought to the good Doctor’s mind a letter written by another poet, William Cowper, to his cousin  Lady Hesketh, dated October 10^th 1787, in which he describes the behaviour of a leech he owns,

“Yesterday it thundered, last night it lightened, and at three this morning I saw the sky as red as a city in flames could have made it. I have a leech in a bottle that foretells all these prodigies and convulsions of nature. No, not as you will naturally conjecture, by articulate utterance of oracular notices, but by a variety of gesticulations, which here I have not room to give an account of. Suffice it to say, that no change of weather surprises him, and that, in point of the earliest and most accurate intelligence, he is worth all the barometers in the world.”

William Cowper - Letter to Lady Hesketh - 1787

Merryweather began to observe leeches, and noted that some, but not all, would indeed crawl upwards in the bottle in which they were kept prior to a thunderstorm. He selected those that were, in his opinion, the most prescient and put a dozen of them (his ‘jury of philosophical counsellors’) into pint bottles, which he arranged in a circle so that the leeches could see each other and not suffer the ‘affliction of solitary confinement’. 

The Medicinal Leech

In the neck of each bottle he placed a metal tube, into which the leech could crawl, and attached to each tube was a small whalebone trigger, which was dislodged by the movement of the leech. This, by means of a mouse-trap like contrivance, caused a spring-loaded hammer to strike a bell placed at the centre of the circle of bottles. The ringing of the bell indicated the advent of a thunderstorm, and the more times the bell rang, the greater the likelihood of a storm. Merryweather deduced that the leeches were acting due to a change in atmospheric electricity prior to inclement weather, and he toyed with the notion of calling his device The Atmospheric Electro-Magnetic Telegraph Conducted by Animal Instinct but thought better of it and called it instead his Tempest Prognosticator –

“… two words expressive enough for all foreigners to understand.”

The Tempest Prognosticator

Dr Merryweather was a surgeon in Whitby, Yorkshire and a member of the Whitby Literary and Philosophical Society, to whom he unveiled his invention in a three-hour presentation on February 27^th 1851. 

G Merryweather - An Essay Explanatory of the Tempest Prognosticator

The tone of the paper is excellently maintained throughout –it is erudite and suitably scholarly, meticulously referenced and learnedly footnoted, and rambles off in unexpected directions only to be brought expertly back to its subject, and it is all done with a tongue held very firmly in cheek. Merryweather was having a very good time with his Tempest Prognosticator, and having picked up his ball he certainly ran with it. 

Merryweather's Letter

He wrote a letter to the committee that was organising the Great Exhibition of 1851, asking if he might have space to present this great benefit to humanity (with a wonderful proviso that his device be protected from potential piracy whilst on display) and, perhaps to his surprise, he was given permission to take it to London. The Great Exhibition opened on May 1^st 1851 and Dr Merryweather’s Tempest Prognosticator was shown to the world. Constructed from French-polished mahogany, polished brass, silver, ivory and glass, and fashioned like an Indian temple, it was a great success. 

Detail of a replica Tempest Prognosticator

Merryweather applied to the Admirality to have his machines installed at sea ports but for some strange reason his application was declined, the Navy Board plumping instead for Robert Fitzroy’s Storm Glass Barometer.  The original mechanism has been lost, but replicas have since been made (notably for the 1951 Festival of Britain).

Build Your Own Tempest Prognosticator