. The London, Edinburgh and Dublin philosophical magazine and journal of science . the measurement of the of the couple. The two vessels and are fitted up in all respectsalike. As will be seen later, the indications of these thermopilesare used in determining small correction-terms in the ex-pression for conductivity. It was therefore necessary tocalibrate them with thermometers; but high accuracy wasnot required. The piles in use were read by the deflexionthey produced on a mirror galvanometer, and the differenceof temperature corresponding to 1 cm. deflexion was foundto be R
. The London, Edinburgh and Dublin philosophical magazine and journal of science . the measurement of the of the couple. The two vessels and are fitted up in all respectsalike. As will be seen later, the indications of these thermopilesare used in determining small correction-terms in the ex-pression for conductivity. It was therefore necessary tocalibrate them with thermometers; but high accuracy wasnot required. The piles in use were read by the deflexionthey produced on a mirror galvanometer, and the differenceof temperature corresponding to 1 cm. deflexion was foundto be JK . . 0-516° 0. JF . . JK . . 0-541JF . . 0-602The constant of the galvanometer was tested each day, butdid not vary appreciably. the Thermal Conductivity of Water. 53 Calibration of Heating-Coils as Thermometers. Attempts to calibrate these in stirred oil within the smallrange of temperature they were to measure not being verysatisfactory, this was done by completely enclosing them inmetal water-jackets (J, J, fig. 4) arranged in series and sup- Fig. plied with a steady stream of cold water. A difference of tem-perature between the jackets was produced by heating thespiral tube S, and the difference was measured by two mercurythermometers immersed in them, and divided to tenths of adegree. The opposing arms of the bridge were the coils b a, a bof fig. 3, connected as in the actual conductivity measurements,so that the bridge-wire itself could be calibrated directly intodegrees. This wire (A A) is of platinoid, 0*7 mm. thick, inparallel wdth five thick wires of german-silver, and its resist-ance is 0*0003280 ohm per cm. To increase its effectivelength (necessary for the calibration) two other sets of wires inparallel (B and C, fig. 4) were connected to it in series bymercury commutators P and Q. These commutators were soarranged that A A could be inserted in the middle or placedat either end of B and C. To eliminate thermoelectric effects the contact-maker D
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