--- title: "Whitby doctor’s 1851 leech barometer used 12 leeches to ring a storm bell at the Great Exhibition" url: https://badiyaa.com/tempest-prognosticator-leech-barometer-merryweather/ published: 2026-11-08T06:33:00+00:00 modified: 2026-11-08T06:33:00+00:00 section: History publisher: Badiyaa --- # Whitby doctor’s 1851 leech barometer used 12 leeches to ring a storm bell at the Great Exhibition George Merryweather wired a dozen leeches in pint bottles to tiny hammers, pitched the idea for Britain's coasts and lost out to FitzRoy's storm glass. In 1850 a Whitby doctor named George Merryweather put twelve leeches into twelve pint bottles, wired each one to a tiny hammer, and asked them to warn Britain about storms. When a leech grew restless and crawled up into the metal tube at the neck of its bottle, it knocked loose a piece of whalebone and the hammer struck a bell. More rings meant a likelier storm. He called the machine the Tempest Prognosticator. The idea is going around again online, 175 years later, and it still sounds like a joke. It was not one to its inventor. ## A poem, a museum curator and a jury of leeches Merryweather was the honorary curator of the museum run by the Whitby Literary and Philosophical Society on the North Yorkshire coast. He had noticed that medicinal leeches seemed to react to changes in the air before bad weather. His spark came from verse: two lines in Edward Jenner’s poem Signs of Rain describe a disturbed leech climbing “to the summit of his prison.” His working title was a mouthful: “An Atmospheric Electromagnetic Telegraph, conducted by Animal Instinct.” He described the leeches as his “jury of philosophical councilors,” and he arranged their bottles in a ring so that, in his telling, no leech would suffer the affliction of solitary confinement. His own description of the setup survives in the essay he later printed: > “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 Whitby to the Great Exhibition Here is the short timeline of how a seaside doctor’s leech bell reached the biggest show on Earth: - **1850:** Merryweather tests the device all year and posts storm warnings to Henry Belcher, president of the Philosophical Society. Records of 28 predictions are kept in the Whitby Museum library. - **27 February 1851:** He reads members an essay on the machine that reportedly runs close to three hours. - **1851:** The most ornate of his six designs, built by Whitby craftsmen and modeled on Indian temple architecture, goes on show at the Great Exhibition in London’s Crystal Palace. - **1951:** The original having vanished, a replica is built for the Festival of Britain from the printed essay and an old copperplate drawing, then given to Whitby. Merryweather dreamed big. He pictured cheap versions at stations all around the British coast, run by officers beside the lifeboats. “Mr. President and Gentlemen, you will perceive that I am ambitious,” he told the society. ## Why the government said no He lobbied officials to adopt his prognosticator for coastal warnings. They chose Robert FitzRoy’s storm glass instead. There is no record that any of the six designs was ever put to practical use, and the original machine disappeared after the exhibition closed. What makes the story land today is the gap between the method and the ambition. A doctor took a line of poetry about a twitchy worm and tried to turn it into a national early-warning network, complete with an inspector of stations. Modern forecasting runs on satellites and pressure readings, yet the impulse behind the leech bell, watching animals for clues about the weather, is far older than Merryweather and still shows up in folk sayings about cows lying down before rain. ## Where to see one The 1951 replica still sits in the main hall of Whitby Museum, in a glass case on a table three feet across. Working copies were later built from its plans and photographs, including one displayed at the UK’s National Meteorological Library and Archive in Exeter and another at the Barometer Museum in Okehampton, Devon. Merryweather was curator of the Whitby museum twice, from 1840 to 1843 and again from 1847 to 1861. The leech machine is the one exhibit of his that people still travel to see. ## Further reading - [Wikipedia: Tempest prognosticator](https://en.wikipedia.org/wiki/Tempest_Prognosticator) *Image: Neil Theasby, CC BY-SA 2.0 via Wikimedia Commons* *This article was produced with AI assistance and reviewed by our Editorial Desk. [How we work](https://badiyaa.com/editorial-policy/).*