FOUCHER, [Simon].

Traité des Hygrometres ou machines pour mesurer la secheresse et l’humidité de l’air. A Paris: Chez Estienne Michallet… 1686.

Price £ GBP 900.00

12mo, 195 [i.e. 166, pagination erratic towards the end] pages, 1 leaf (contents), 1 folding engraved plate. With woodcuts in the text. Contemporary speckled calf, spine gilt in compartments. Early signature of Vauville on front endpaper, signature of La Ducquérie twice on title-page.

FIRST EDITION of a scarce book on hygrometers. Foucher describes in this work a method of indicating humidity by using cords of sheepskin and measuring their changes in length or their twisting and untwisting. He also describes “another hygrometer that seems to have been unique… Remembering the behaviour of drum heads, he stretched a piece of parchment over a box and measured the motion of the centre by means of a lever of large magnification. A small weight kept the parchment taut” (Middleton, Invention of the meteorological instruments, p. 95). There is also an account of a hygrometer invented by Robert Boyle on pages 72–73, with an illustration.

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