Written for Brought to Light by: Maria Blackmore and Ella Roberts. Student research group: Holly Crothers, Maria Blackmore, Corey Blackmore, Zane Garland, Ella Roberts.

Thermopile - Bismuth & Antimony. Brass instrument mounted on a column, attached to a meta circular base.

A thermopile is a scientific instrument used in physics to convert infrared radiation, or heat, into an electrical signal. This thermopile is an array of 56 bismuth and antimony junction pairs, known as thermocouples connected in series, and appears inside the cone as a flat 7 by 8 block of alternating metal pairs. One junction is kept cold by the metal block in the back of the conical, which attracts heat, and the other junction is warmed by the infrared radiation. The difference in heat causes a potential difference, or voltage, across the two metals which can be accessed via the terminals on the base. This signal is typically small, hundreds of millivolts, and it mostly used for the measurement of temperature and thermal radiation.

This thermopile was created circa 1880, 45 years after its invention by Leopoldo Nobili and Macedonio Melloni in 1835. Many instrument manufacturers were making variations of thermopile models during this time hence they were very accessible.

The thermopile is very likely to have been used by Lamb, and succeeding professors, during physics lectures and workshops. In particular the 1877 University Calendar states Lamb taught ‘the elements of the science of heat’ and ‘Maxwell’s theory of heat” with each course “as far as possible illustrated by experiment”, the thermopile was most likely used in these demonstrations.