Accession No

1933

Brief Description

wet and dry bulb hygrometer, by L. Casella, English, 2/2 19th Century

Origin

England; London

Maker

L. Casella

Class

meteorology

Earliest Date

1850

Latest Date

1900

Inscription Date

Material

wood; metal (brass, mercury, steel, oxidised brass); plastic

Dimensions

length 350mm; breadth 170mm; thickness 43mm

Special Collection

Cavendish collection

Provenance

Transferred from the Cavendish Laboratory, University of Cambridge in 1974.

Inscription

‘L. CASELLA, maker to the admiralty & ordnance, LONDON’ (both scales)

Description Notes

Wooden frame supporting one round-bulb (dry) Celsius mercury in glass thermometer and one long-bulb (wet) centigrade mercury in glass thermometer. Scales divided 10 - 120 numbered by 10, subdivided to 5. Scale marked on dry (left) thermometer subdivided to 1˚. Wet thermometer is a replacement (stamped ‘BTD’) and has a scale divided [-5] - [1]10˚ C, numbered by 10˚, subdivided to 1˚. Oxidised brass (?) bracket mounted on right hand at base. Brass bracket and keyhole mounts on wooden frame.

NOTE: glass pot for water for wet bulb is missing.

Condition fair; incomplete (wet thermometer a replacement; glass pot for water for wet bulb is missing)

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:42196