Students of the history of meteorology may be aware of the Tempest Prognosticator of Dr. George Merryweather, but it was news to me. The Tempest Prognosticator was a device invented in the mid-nineteenth century that allowed the forecast of storms, via leeches. Apparently there's been some debate about whether this contraption actually existed, but author Paul Collins, on his blog, confirms that it did. In fact, it was displayed at the Great Exhibition of 1851. Here's how it worked:

The "Tempest Prognosticator" consisted of twelve pint bottles of white glass, round the base of a circular stand, at the top of which was a bell surrounded by twelve hammers. Each bottle was connected with one of the hammers through a metal tube in its neck, containing a piece of whalebone and a wire, to which was attached a small gilt chain. Here is the inventor’s description of how the Prognosticator works: "After having arranged this mouse trap contrivance, 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."

Paul Collins also reports that some guy has built a working replica of the Prognsticator, and has it on display at the Barometer World Museum in Devon, England. No word on whether it actually worked.