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" High Temperature Measurements,” by Le Chatelier and Boudouard, translated by Burgess.

The essential part of these pyrometers consists of two fine wires of different metals or alloys fused together at one end and connected to a galvanometer or millivoltmeter at their other ends, the fused end being inserted in the source of heat. An E.M.F. is developed by the difference in temperature of the two ends of the couple, this being roughly proportional to the difference in temperature. The most satisfactory couples have been shown to be platinum against platinum alloyed with 10 per cent, rhodium for temperatures up to 1,600° C., and platinum against platinum 10 per cent, alloyed with iridium for temperatures up to 1,000° C.

In commercial work a high resistance millivoltmeter is employed, so that the instrument may be set up at a considerable distance from the source of heat without the necessity of making allowance for the resistance of the conducting wires. The millivoltmeter scales are also calibrated in temperature degrees ; a fixed or portable instrument can be supplied.

Thread Recorder. (Fig. 15.)

(1) " On Methods for the Continuous (Photographic) and Quasi-Continuous Registration of the Diurnal Curve of the Temperature of the Animal Body,” by A. Gamgee, Phil. Trans. Roy. Soc., Series B., Vol. 200, page 239, /1908.

(2) “ Engineer,” June 14th, 1907.

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FIG. 15.

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