SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Vegetable hygrometer, 19th-century artwork. Hygrometers are used to measure relative humidity, which can be used to predict the approach of rain. Several types of plant materials absorb moisture from the air, and can be used to form what is called a 'vegetable hygrometer'. This is a French version, labelled with rain ('pluie') and good weather ('beau temps'). The plants and their appearances when wet (right) and dry (left), are: 1. Carline thistle; 2. Water moss; 3. Pine cone; 4. Erodium seed; 5. Feathered stipe. Artwork from the 13th volume (first period of 1894) of the French popular science weekly 'La Science Illustree'.
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