An instrument used in the mid-20th century to record rapid temperature changes in the ocean. It consisted of a constantin wire soldered to copper wires in two places. One junction was exposed to the sea water, and the other embedded in compact insulation material. The thermoelectric current induced depended on the temperature difference between the two junctions, and was indicated by means of a remote galvanometer. This instrument therefore measured the temperature difference between the sea water and the insulated junction rather than the temperature itself.