Images(2)

radiant heat differential thermometer

Date1850-1900

Inventory Number1998-1-0752

ClassificationThermometer

Subject

Maker English ?

User Department of Physics, Harvard University founded 1884

Cultural Region

Dimensions19 x 9.5 cm (7 1/2 x 3 3/4 in.)

Material

Accessoriescracked glass cover

DescriptionA radiation thermometer held vertically by a small brass cup that rests on a turned wooden base. The thermometer consists of a thin glass tube with spherical, air filled bulbs at both ends, one of which is tinted black. The thermometer bends 180 degrees near its middle such that its two bulbs end up close to each other, at the top of the thermometer. As one section is slightly shorter than the other, the black bulb ends up higher than the other and the tube bends again so that they are aligned one after the other above the parallel sections of the tube. A white ivory backing is attached with brass brackets to both sections of the thermometer and it has a scale near the section with the black bulb at the end. Its range is from 0 to 90 degrees increasing downwards.

The thermometer comes with a cylindrical glass cover that fits the brass cup, which is currently cracked. White "R" painted on the base below the old label mentioning a series of numbers: "8-9-32".

Signedunsigned

Inscribedold label: Differential thermometer with clear and black bulbs for measuring radiant heat introduced in England in 1803 by Prof. John Leslie / Mr. Anderson 1980 South Kensington

Curatorial RemarksThough this instrument appears to be coming from England, the "8-9-32" number on the label is very similar to the ones found on instruments used in the department of physics at Harvard. Idem for the "R" painted in white.

FunctionThis is a thermometer that measures the amount of heat (infrared radiation) emitted by a hot body or the sun. Its thin tube is filled with a liquid, while the two glass bulbs are filled with air. As one of the two spheres is tinted black, it will get hotter than the other one as it captures radiation more efficiently. This will make the air in that bulb expand more than the one in the other one, and push the liquid downwards. As a consequence, the height of the liquid on the scale will be proportional to the amount of heat radiation present.

ProvenanceAs mentioned on old label, "Mr. Anderson 1980 South Kensington [London, UK]".