c1885 British Immisch Patent Cased Silvered Thermometer Fob


A rare c1885 British Immisch Patent Cased Silverplated round miniature Thermometer Fob in very good working condition.
It consists of a round Silverplated pocketwatch style thermometer, with a 2.5 cm (1inch) diameter white face, with a Fahrenheit scale going from 27 to 114 degrees. At the base of the face is marked PATENT and the scale has a red marker for body temperature of 98 degrees. The thermometer has a suspension ring in order to attach it to a Fob chain and comes with its leather covered fitted wooden case.
The Immisch thermometer works on the basis of a miniaturised jewelled movement based on an alcohol filled Bourdon tube, constructed principally in brass and tensioned on a blued steel hair spring, with amplification by levers and mounted between two plates and rack and pinion transmission to pointer needle on the face.
The British patent was granted to Karl Moritz Immisch in July 1881 and was generally received with great acclaim. This system, based upon a Bourdon tube applied to temperature measurement, was considered the finest of its mechanical type, in its time. It received many awards and has stood the test of time. Held in the hand, or more correctly to the wrist, it responds almost immediately, showing very good sensitivity. It appears to be accurate as well.
Mechanical thermometers manufactured in the 19th century are rare, predominantly as they were substantially more expensive than the simple mercurial thermometer. There was also some general reluctance to accept that they could be as accurate.
Size thermometer: 2.7 x 4 x 1 cm (1 x 1 ½ x 3/8 inches)
Size case: 4.5 x 6 x 2 cm (1 ¾ x 2 3/8 x ¾ inches)
Weight: 26 g