Tempest Prognosticator

The Tempest Prognosticator, also known as the Leech Barometer, is an 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.

Dr. Merryweather, honorary curator of the Whitby Literary and Philosophical Society's Museum, detailed the sensitivity that medicinal leeches displayed in reaction to electrical conditions in the atmosphere. He 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."[1] Merryweather spent much of 1850 developing his ideas and came up with six designs for what he originally referred to as "An Atmospheric Electromagnetic Telegraph, conducted by Animal Instinct". On 27 February 1851 he gave a near three-hour essay to members of the Philosophical Society entitled "Essay explanatory of the Tempest Prognosticator in the building of the Great Exhibition for the Works of Industry of All Nations". Merryweather referred to the leeches as his "jury of philosophical councilors" and also noted other features of the design, including the fact that the leeches were placed in glass bottles placed in a circle to prevent them from feeling "the affliction of solitary confinement".