Plate from 'Traittez des Barometres, Thermometres et Notiometres ou Hygrometres' (1688) by J D'Alence. A natural philosopher is shown demonstrating how a column of water can be raised and lowered in a glas tube by manually warming the air trapped in the upper flask. The instrument is thus behaving like an air thermometer rather than a barometer. This book is a pocket-sized treatise on the barometer, thermometer and hygrometer. Its plates are particularly early illustrations of natural philosophers at work.
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