Accession No


Brief Description

Combined dew point and wet-and-dry hygrometers, Fastre aine, 1851


Rue de l’Ecole Polytechnique 3; Paris; France


Fastre aine



Earliest Date

Jan. 1, 1851

Latest Date


Inscription Date


metal (brass, silver, steel, mercury); glass


box length 379mm; breadth 175mm; height 51mm

Special Collection


Purchased from Peter Delehar, London, England, 12/1978.


‘Fastre aine, Rue de l’Ecole Polytechnique 3, a Paris. 1851’ (on base)
‘Fastre aine a Paris 1852’ (on one thermometer)
‘Secretan a Paris (Aout 1871).’ (on other thermometer)

Description Notes

Combined dew point and wet-and-dry hygrometers, Fastre aine, 1851.

The wet-and-dry hygrometer consists of two long-bulb mercury in glass thermometers, one with opal back signed Secretan à Paris (Août 1871). Combined Regnault Condensation hygrometer and Mason Wet and Dry Bulb hygrometer. Brass base (two parts), brass stands (3 parts), brass fittings (3 parts and 2 screws), 3 glass tubes (2 partially silvered, corked and with brass fittings), steel screw/bradall (2 parts), 2 mercury thermometers (3rd thermometer now missing). In fitted lined box.

Condition: good.


Allison Ksiazkiewicz; 'Measuring Air Humidity'; Explore Whipple Collections online article; Whipple Museum of the History of Science; University of Cambridge:


This fitted case holds two types of hygrometer, an instrument to measure the humidity of the air.

Two thermometers can be set up on the stand as a wet-and-dry bulb hygrometer. In use, one thermometer bulb is wrapped in muslin which is kept damp by dipping into a small pot of water. In dry air the wet muslin evaporates rapidly, cooling the thermometer bulb, giving a different temperature reading to the dry-bulb thermometer. In humid air there is little evaporation and the two thermometers have a similar reading.

The long-bulb thermometers can be set up as a Regnault dew-point hygrometer. The dew-point is the air temperature at which moisture will condense. Here air is bubbled through the ether filling the sheath of one thermometer, cooling its bulb. Dew will form round the bulb sheath, at a temperature depending on the humidity of the atmosphere.

The French scientist Henry Victor Regnault devised his hygrometer in 1845, probably without realising that it resembled one described by Johann Wolfgang Dobereiner in 1822.

This example was made by the Parisian instrument maker Fastré in 1851. A replacement thermometer was added in 1871.

Created by: Dr. Anita McConnell on 26/03/2008


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