The inscription on the face of this circular metal hygrometer—“Made in Germany / D.R. P. No. 16568 / Hygrometer”—refers to the German patent issued to Otto Mithoff, an engineer in Berlin, in 1881. Other inscriptions read "Outdoor Fluctuations" and "Indoor Fluctuations" and there is a scale running from Full Saturation to Absolutely Dry. This English wording suggests that this example was designed for sale in England or the United States.
Ref: Otto Mithoff, “Hygroskop aus der Inneren Haut der Eierschlen hergestellt,” German Patent 16568 (March 18, 1881).
“Hygroskop von O. Mithoff in Berlin,” Dingler’s polytechnische Journal 245 (1882): 452.
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