A Natural Barometer

The article below from the Isle of Wight Observer of 1892 makes interesting reading:

One of the most curious of the many natural barometers consists of a half pint glass half full of water, a piece of muslin, and a leech. The leech must be put in the water, and the muslin tied over the top of the glass so that the creature cannot get out again. When fine weather is to be the order of the day the leech will remain at the bottom of the water, coiled up in a spiral shape, and perfectly motionless. If rain is to be expected it will keep to the top of the glass, and remain there until there is a likelihood of more settled weather. If there is to be a storm of wind the little animal will contort itself violently and squirm about. For some days before thunder it will keep out of the water almost all the time, and will occasionally move its body in a convulsive fashion. For frosty weather it behaves in the same manner as for fine, and it fortells snow in the same manner as it does rain.

The idea in this article relates to the Tempest Prognosticator or Leech Barometer, 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.

Merryweather came up with six designs ranging from cheap versions to a more expensive design which featured the architecture of Indian temples and was shown in the 1851 Great Exhibition at The Crystal Palace in London.
Merryweather 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.”

Sources: Isle of Wight Observer 23 April 1892; information and image of Tempest Prognosticator from wikipedia