Resistivity of Mercury at the Temperature of Liquid Air. 79 



Adopting the value for the specific resistance of pure mercury at 

 C., which has been recommended by the Board of Trade Electrical 

 Committee, viz., 94,070 C.G.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 plati- 

 num scale the resistivity curve again changes direction, and con- 

 tinues 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 pt. 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 condi- 

 tion, 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 tem- 

 peratures of 197-9 and 97, the mean increase in resistivity is 



