. A new thermo-electric fluid-meter and hot-wire anemometer. the following page, and israther unusual in that its inversion tenrperatureoccurs at about 40° C» In this respect its behavioris somewhat similar to that of copper-zinc, the in-version temperature of which comes to 30° 0, Anothercombination, which has its inversion temperature near0°, is iron cadinum, and its inversion temperaturecomes at 170°. Prom the appearance of the accompanyingcurve for the copper-tungsten couple, it is inferredthat the thermoelectric curve is not a true parabola,as was also observed by Dewar and Fleming on num
. A new thermo-electric fluid-meter and hot-wire anemometer. the following page, and israther unusual in that its inversion tenrperatureoccurs at about 40° C» In this respect its behavioris somewhat similar to that of copper-zinc, the in-version temperature of which comes to 30° 0, Anothercombination, which has its inversion temperature near0°, is iron cadinum, and its inversion temperaturecomes at 170°. Prom the appearance of the accompanyingcurve for the copper-tungsten couple, it is inferredthat the thermoelectric curve is not a true parabola,as was also observed by Dewar and Fleming on numerousother metals, (See Dewar and Fleming in Phil. Mag,40, p, 95, 1895), For temperatures below -100° C,the thermoelectric power of tungsten against copper isabout 3,5 to 4 microvolts per degree, — 200° C, thethermoelectric power is about 4,5 microvolts perdegree, so that tungsten, like tantalum shows noapparent advantage in thermocouple work, *5|c)f:>>:**5|c+ + *+*****?** ****** /i/>f£/^OAt £ ?-£/< &\ /OO 1 i -JOO. ^OOQO rjETAf/s/i/^ ra/^£. 160 MEASUREMEIIT OP VEHY SMALL CURRENTS BY MEAES OPTHERMOELEMENTS 7H SPECIAL REPEREKCE TO RADIO CIRCUITS, There are yariotia methods ueed for themeasurement of currents of a few milllamperes orless, Suoh measurements may be made by the use ofthermal ammeters of various types, and in general,are free from some of the dlffioultieB experiencedin the measurement of larger currents, principallybecause conductors of very small cross sections maybe used the resistance of which does not vary withthe frequency of the current under measurement. Thevarious types of thermal ammeters employ the follow-ing principles: Grossed-Wire Thermal-elements,Self-Heated Thermoelement, Thermo-galvanometer Volo-meter. Instruments operating on these variousprinciples are described below. Prior to the war thermoelectric cotipleshad been employed for measuring low values ofalternating ctirrent. These couples were almosteTolusively of
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