One of the most peculiar and fascinating devices of the nineteenth century was to be found at the Great Exhibition of Nations in Crystal Garden in 1851, a device that encapsulates the very best and the strangest of our magnificent era. The contraption in question was named the Atmospheric Electromagnetic Telegraph conducted by Animal Instinct, or to use the truncated title: The Tempest Prognosticator; a living bio-machine that could predict the weather – the stuff of science fiction.

And it was powered by leeches.

Small slug-like, squishy, fecal-shaped, vampiric creatures, dwellers of rivers and ponds and other dark places. Find one attached to you? Don’t remove it by pulling it off, for goodness sake. Try that, and the leech will reward your arrogance by vomiting the contents of it’s stomach into your bloodstream, infecting you with all manner of contaminants. Oh my no, you’ll have to burn it away, like a witch-infested hamlet in a medieval France. Delightful little things.

And what did mankind say when they first saw these repulsive creatures? Did they move to a safe distance whilst vowing to stamp them all flat on sight? Of course not. “Those,” they said, scooping them into jars by the handful, “those could be used for something useful.”

As if to prove the point, they immediately started attaching them to sick people to drain ‘excess blood’, because that was claimed to fix almost any ailment for fifteen hundred years. It seemed to work of course, because if the average patient saw what the doctor was about to affix to their skin in the name of wellness, I’m certain many people would exclaim: “Oh, will you look at that, my headache cleared right up. Thanks anyway. Cheerio Doctor!” whilst exiting the premises as quickly as possible.

That said, it appears that there are uses for leeches other than draining blood, or getting attached to an intrepid explorer’s inner-thigh somewhere in a jungle river. A Yorkshire inventor by the extremely appropo name of Dr. George Merryweather believed he could harness into a machine the very nature of animal instinct to predict meteorological events such as storms, with the intention of alerting coastal areas and shipping concerns. Thus the Tempest Prognosticator was conceived.

In a structure akin to a fairground carousel, but with bottles of leeches instead of horse-riding children (although the comparison between blood-sucking parasites and those tiny humans is hard to ignore), the device was three feet wide by four feet tall and crowned by an artisinal bell. The bell held little twelve little hammers with wires that led down to a rotunda of twelve glass pint bottles, each containing a single leech.

Purportedly disturbed by barometric and electromagnetic changes in the upper atmosphere, these little amorphic creatures would climb the side of the bottles, disturbing a whale-bone trigger that pulled on a small chain and caused the ringing of the bell. Enough leeches triggering the bell with enough frequency, and it’s time to don your rain gear.

Dr Merryweather, a competent inventor he may have been, was rather too attached to his medicinal grade Hirudo medicinalis leeches. In his treatise on the machine Essay Explanatory of the Tempest Prognosticator, read before the Whitby Philosophical Society (and a thrilling three hours that must have been), he espoused the integral role of the leeches. The little blood-engorged blobs were, as he says:

“…capable of attachment […] for after they become acquainted with me, they never attempt to bite me; but some of them have […] thrown themselves into graceful undulations when I have approached them; I suppose an expression of their being glad to see me.”

How touching. He discovered however to his chagrin that not all leeches were made equally and some were certainly not up to the task of detecting changes in the weather. One envisions that there might have occurred something akin to a professional falling-out between Dr Merryweather and some of his leeches when he stated:

“…some appeared to be more sensitive and prophetic than others; and some appeared to be absolutely stupid.”

Now, steady on Doctor, give the poor thing a chance. Might have been its first day.

On the most part, Merryweather’s sensitivity towards his ‘companions’, as he put it, was rather endearing. Seeing himself as a ‘self constituted judge’ surrounded by this meteorological ‘jury of philosophical counsellors’ (he’s still talking about the leeches here, in case you were confused), he arranged the captive leeches contained in their bottles in a circle so:

“…that the leeches might see one another, and not endure the affliction of solitary confinement.”

His attachment (forgive the pun) to his beloved wards aside, Dr Merryweather may have lost a little too much blood in feeding the leeches, as his essay describes plans for the device that are extraordinarily ambitious in scope. He had intended for his ‘Lilliputian revolving temples’ to protect shipping and coastal towns against the severe storms that batter those regions, suggesting that they might be placed on all coasts, and also distributed throughout the world.

“If we had such a staff of officers, aided by such means, it is impossible to estimate the advantages and blessings that would be obtained to the British Nation.”



This peculiar and yet beautifully designed machine was showcased at the ‘Great Exhibition of the works of Industry of all Nations’, the first international exposition of manufactured items held in 1851 at Crystal Palace, London. Although Merryweather stood by the veracity of his creation, the scientific accuracy of the polished mahogany and brass instrument has not been proven, and the fate of the machine following the conclusion of the event is not known. What we do know is that the lowly leeches, not only losing favor at the time in the medical field, also found themselves robbed of employment in the weather-prediction industry, as barometers and other devices took precedence.

Otherwise, who knows, if Dr. Merryweather had achieved success:

“…I could cause a little leech, governed by instinct, to ring Saint Paul’s great bell in London as a signal for an approaching storm.”

This would create a singularly peculiar circumstance where impulsive, blood-sucking, parasitic creatures would be running affairs of great importance in the capital. Although, it could be said that British Parliament is that ambition already achieved…

(Sources available on request)

Dr. J.D.T. Pembroke – surgeon, physician, alienist; these are the collected writings of the doctor’s demented journals and articles as he studies the peculiar, disturbing and strange history of medicine and macabre through the ages. You can find more of his musings, papers and articles here.

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