A Leeds and Northrup Catalogue number 8632-C Optical Pyrometer. There were a large number of these pyrometers manufactured with slightly different temperature ranges. The “C” series were calibrated for the Celsius scale. The instrument box measures 18cm by 18 cm by 25 cm while the measuring head, which is attached via a cable, is approximately 30 cm in length. The battery-operated instrument operates on the principle of passing a current through a high-resistance wire in the head. The observer then looks through the head at the wire and simultaneously at the material being observed and adjusts the current until the temperature (and hence the colour) of the wire and the temperature of the material in question match. At this point the outline of the wire disappears – hence the term “disappearing wire pyrometer”. Most of the models developed by Leeds and Northrup covered three temperature ranges. The range desired was chosen by rotating the end of the measuring head to L, H or Hx. Labels and writing on the instrument indicate that this particular instrument was used at the Whiteshell laboratories in Lab B-15. It is not clear when the instrument was manufactured but similar models were manufactured in the 1950-1960 era.
