Page:Proceedings of the Royal Society of London Vol 60.djvu/94

Rh Platinum temperature, p t, in terms of the standard platinum thermometer PiObserved and corrected resistance of mercury in lead glass spiral in ohms. Resistivity of mercury in glass in O.GLS. units.

- 37-6 0 -6387 80760 - 37-2 0 -6587 83280 - 36-7 0 -6787 85810 - 36 0 0 -7087 89600 - 35 2 0 -7208 91140 - 33-7 0-7228 91380 - 31-2 0 -7248 91640 0 0 -7440 94070 + 13-1 0-7518 95060 + 16-3 0-7540 95330 + 35-4 0 -7653 96760

Adopting the value for the specific resistance of pure mercury at 0° C., which has been recommended by the Board of Trade Electrical Committee, viz., 94,070 C.Gr.S. units, we have reduced the observed resistances of the mercury column at various temperatures to their equivalents in resistivity in absolute units, and placed these numbers against the observed resistances in the table above. As the specific resistance of mercury has been so carefully observed by many observers, we did not, for a moment, consider it necessary to attempt a further determination of this constant. On plotting out these values of the resistivity of mercury in the form of a curve in terms of the corresponding platinum temperatures, we find the resistivity curve has the form shown in fig. 1. It will be noticed that the resistivity of the mercury decreases gradually from the point at which the observations finished, viz., at +35° C., to the temperature —36° on the platinum scale. At this point the resistivity rapidly decreases to about one-quarter of its value in falling from —36° to — 50°, and this sudden change all takes place within the range of about 14° of temperature. At the temperature of —50° on the platinum scale the resistivity curve again changes direction, and continues downwards in such a direction as to show that if produced along the same line from the lowest temperature actually observed, viz., —204° on the platinum scale, it would pass exactly through the absolue zero of temperature on this scale, which is —283° It is also interesting to note that the part of the curve which corresponds to the mercury in the liquid state is almost exactly parallel to that part of the curve which corresponds to mercury in the solid condition, although, owing to the difference in the absolute values of the resistivities at these parts, the temperature coefficients as usually defined are very different. In the solid condition between the temperatures of —197'9° and —97°, the mean increase in resistivity is