Accession No

5184

Brief Description

bimetallic thermometer by Breguet, c.1845

Origin

Maker

Bréguet

Class

thermometry

Earliest Date

1845

Latest Date

1845

Inscription Date

Material

wood (mahogany); glass; metal (brass, mercury), wax, paper

Dimensions

height 180mm; diameter of base 147mm

Special Collection

Provenance

Purchased from Peter Delehar, 146 Portobello Road, London, W11 2DZ, England in 27/10/1997.

Inscription

‘BREGUET’ (on scale)
‘161’ (engraved at bottom of pillar and carved into base)

Description Notes

Mahogany circular base, bearing white printed paper scale, divided 0 - [360] degrees numbered by 10 divided to 1. Curved brass support pillar marked with serial number 161, holds a rod surrounded by a bimetallic helix. There are two pins with red wax ends for adjusting sensitivity. Rod sits in bath which would have contained mercury (?). Zero adjustment is by a knurled knob at the top of the rod. A second knurled knob at the top of the pillar can be used to adjust the helix (?). A glass dome with two locating lugs on a brass rim fits into a circular groove on the base and the lugs slot into brass catches. Two brass terminals (?) protrude from the base.

Condition good; complete

References

Events

Description
A thermometer is an instrument that measures how hot or cold something is, in other words, its temperature. Most familiar is the "Mercury-in-glass" thermometer, but there are many other kinds.

Many materials expand as they get hotter and contract as they get colder . This expansion and contraction can be used to measure the corresponding changes in temperature. Thus the first useful thermometers were made from a glass bulb full of mercury to which was attached a narrow glass tube. As the bulb is heated a fine thread of mercury expands up the narrow tube. Thermometers, requiring great skill in glass working, were first made by Daniel Fahrenheit of Amsterdam in 1717.

To measure temperature precisely, a numerical scale of "degrees" is needed. To provide this scale two fixed points are chosen, such as melting ice and boiling water. Convenient temperatures are then given to these two fixed points: today melting ice is given a temperature of 0 degrees and boiling water 100 degrees. This is the Celsius or Centigrade scale (although it is quite arbitrary). Fahrenheit himself originally chose the coldest temperature that he could produce (a freezing mixture of ammonium chloride and snow) as 0 degrees and body temperature as 96 degrees. This resulted in the Fahrenheit scale in which the freezing point of water is 32° F and the boiling point of water is 212° F.

01/03/2001
Created by: Chris Lewis on 01/03/2001

FM:42131