Bréguet Thermometer

Physics

Accession Number: 2017.ph.739

Description:

This object is a glass dome set in a wood and brass base over a simple mechanism.Two metal terminals emerge at right angles from the wooden base.

The mechanism consists of a brass arm arching up to the top of a vertical metallic pole. Around the post from the top to the base is a helical metallic strip attached at the base to a slender needle. Around the base is a circular scale graduated in 360 degrees and labelled in tens.

The vertical pole sits inside a small metal silver-coloured bowl. Extending down from the metallic helix is a tiny metallic dangling thread.

Alternative Name: Galvanometer

Primary Materials: Glass, Wood, Copper-Alloy

Markings:

On the face of the scale: “BREGUET.”

On the brass supporting arm: “B4037”

On a label attached to the object: “PHY184”. This number refers to the original catalogue.

Dimensions (cm): Diameter=14cm, Height=23cm

Function:

Although this instrument was initially designed as a thermometer, this example has additions by the instrument makers to act as a galvanometer (measurement of electrical current).

As a thermometer, the metallic helix, a bimetallic strip, expands and contracts with the temperature, turning the needle.

As a galvanometer, a small quantity of mercury can be put in the small bowl at the base of the helix. The tiny metallic strip danging into the bowl contacts the mercury enabling an electrical circuit to be run through the helix. The resistivity of the helix causes a change in temperature, thus allowing measurement of the intensity of the current.

Condition:

Excellent. The superficial surface condition of the thermometer and its internal components is excellent, aside from some dust and a few marks on the glass dome. The helix is somewhat misshapen, possibly from repeated use.

The bowl at the base of the helix is silver, possibly from contact with mercury.

Manufacturer: Breguet, Paris

Date of Manufacture: 1886

Provenance:

This Bréguet’s thermometer was purchased by the University of Toronto Department of Mathematics and Physics in 1886, by professor James Loudon through his Paris contact instrument maker Rudolph Koenig. Upon arrival, it became part of the instrument cabinet of the physical laboratory at University College.

It has been retained at the Department of Physics since.

Additional Information and References:

Designed in the early 19th century as a thermometer by the watchmaker Bréguet, this instrument was adapted by Auguste de la Rive 1830s for use as a galvanometer for measuring electrical current in investigations in the still-new field of electrochemistry.

Concerning his alterations, de la Rive wrote:

“J’ai trouvé que, lorsqu’il s’agissait de courans peu intenses, l’appareil precedent n’etait pas sensible. Je l’ai donc remplace avec beaucoup d’avantage dans ce cas, par celiu qui est represente a la fig. 13. C’est un thermometre metallique de Breguet, auquel j’ai fait subir queles legeres modifications pour l’adapter au but que je me proposais.

Il s’agit de faire passer le courant dont on veut etudier l’intensite calorifique, dans l’helice metallique dont les changemens de forme resultant des legeres differences de temperature sont accuses par les degres que parcourt sur unde division circulaie, une aiguille horizontale librement suspendue a l’extrimite inferiere de cette helice. On sait que les degres parcourus par l’aiguille son directement proportionnels aux temperatures auxquelles l’helice est exposee. Pour la mettre dans le circuit, j’ai ajoute a la tige metallique qui porte son extremite superieure un conducteur que l’on met en communication avec l’un des poles de la pile; l’autre pole aboutit au moyen d’un second conducteur, dans une capsule centrale remplie de mercure ou plonge legerement, de maniere qu le frottement soit le moindre possible, un fil fin de platine adapte verticalement a l’extremite inferieure et mobile de l’helice. De cette maniere celle-ci peut etre traversee par un courant quel conque sans etre genee dans les mouvements et dans les changemetns de forme qu’elle doit eprouver en vertue des changemens de temperature.”