Odd this day

3 min readFeb 27, 2023

27 February? That can only mean one thing. YES, THAT’S RIGHT! The anniversary of the day George Merryweather gave a three-hour lecture to the Whitby Literary and Philosophical Society about his leech barometer.

Frontispiece to An Essay explanatory of the Tempest Prognosticator in the building of the Great Exhibition for the works of industry of all nations, read before the Whitby Philosophical Society February 27th, 1851 by George Merryweather MD

The following month, the Weekly Dispatch described it as

a circular pyramidal apparatus of three feet in diameter, and three feet six inches in height, composed of French polished mahogany, silver, brass, &c.

A photo of the Tempest Prognosticator in Whitby Museum. There is no alt text because it would be impossible to make it short enough, and its eccentric workings are described below

Which is true, but it also has 12 pint bottles in it, which would each have contained 1.5in of rainwater, and one leech. A mechanism of wire, whalebone and gilt chain connects each bottle to a bell at the top.

Illustration: “How the Tempest Prognosticator worked, with increasing atmospheric pressure, the leech touches the whalebone button and so causes the hammer to ring the bell.” Illustrated London News Exhibition Number, May 26th 1951

Merryweather called his device The Tempest Prognosticator, and said he got the idea from a poem by Edward Jenner (yes, the one who invented vaccines) called Signs of Rain, two lines of which read:

The leech, disturb’d, is newly risen. Quite to the summit of his prison.

Being a Proper Scientist, though, he didn’t just rely on one source. No, apparently, he was also reminded of a letter from William Cowper to his cousin Lady Hesketh in 1787:

Yesterday it thundered, 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 …he is worth all the barometers in the world.

So, he started studying leeches to see if they would crawl up a bottle before a thunderstorm, selected the ones which displayed an aptitude for the task, and constructed his marvellous mechanism. Wasn’t it cruel, though? Apparently not:

I took it into my head to surround myself with a jury of philosophical counsellors, which was composed of twelve leeches, each placed in a separate pint bottle of white glass, about three inches in diameter, and seven inches in height. I then placed these bottles in a circle, in order, that the leeches might see one another, and not endure the affliction of solitary confinement.

So, the perfectly happy leeches — Merryweather called them his “little comrades” — would be “acted upon by the electrical state of the atmosphere”, climb up, move the whalebone and ring the bell.

Illustration of prognosticator shows 12 bottles arranged in a circle in an ornate circular frame, with wires from each bottle reaching to a bell apparatus at the top. The whole thing is — as one would expect from the Victorians — far more beautiful, or at least less plain, than it needs to be — Image: Wellcome Collection

He even apparently, suggested that

he could cause a little leech, governed by its instinct, to ring St. Paul’s great bell in London, as a signal for an approaching storm.

Oddly, no such device was ever constructed.

Perhaps it was the length of the lecture that did for him. As Prince Philip observed of sermons:

The mind cannot absorb what the backside cannot endure.

Or perhaps perfectly normal barometers had been available since around 1810.

A perfectly normal barometer on a wooden board

Poor George. Still, you can see his Tempest Prognosticator in Whitby Museum, and ponder an alternate universe in which warnings of storms like Otto come via predatory worms and St Paul’s Cathedral.

Odd this day

Written by Coates

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