Editing Hygrometer (section)

=== Hair tension hygrometers ===
[[File:Whalebone hygrometer-MHS 1085-P4070321-gradient.jpg|thumb|upright=0.8|[[Jean-André Deluc|Deluc]]'s hair tension whalebone hygrometer ([[Musée d'histoire des sciences de la Ville de Genève|MHS Geneva]])]]
These devices use a human or animal hair under some tension. (Whalebone and other materials may be used in place of hair.) The hair is [[hygroscopy|hygroscopic]] (tending toward retaining moisture); its length changes with humidity, and [[indicator (distance amplifying instrument)|the length change may be magnified by a mechanism and indicated on a dial or scale]]. Swiss physicist and geologist [[Horace Bénédict de Saussure]] was the first to build such a hygrometer, in 1783. The traditional folk art device known as a [[weather house]] also works on this principle.

{{blockquote|It consists of a human hair {{convert|8|or|10|in|cm|spell=in|disp=sqbr}} long, ''b c, Fig.'' 37, fastened at one extremity to a screw, ''a'', and at the other passing over a pulley, ''c'', being strained tight by a silk thread and weight, ''d''.|John William Draper|''A Textbook on Chemistry'' (1861)}}

The pulley is connected to an index which moves over a graduated scale (e). The instrument can be made more sensitive by removing oils from the hair, such as by first soaking the hair in [[diethyl ether]].<ref>{{cite book |last=Draper |first=John William |title=A Textbook on Chemistry |publisher=Harper & Bros. |year=1861 |page=[https://archive.org/details/bub_gb_HKwS7QDh5eMC/page/n69 55] |url=https://archive.org/details/bub_gb_HKwS7QDh5eMC}}</ref>

{{anchor|Psychrometers}}