436 
PROFESSOR C. H. LEES: THERMAL AND ELECTRICAL 
The results given in the foregoing tables are shown graphically in Plate 30, in which 
the crosses indicate values obtained by observation. To get a more compact diagram 
the scale has been varied to suit the substances tested, and the words which follow 
the names of the substances on the diagram, e.g., “ 1/10 scale,” indicate that the 
values plotted in the diagram are that particular fraction of e.g ., 1/10 of the values 
observed. 
The values found by Jager and Diesselhorst at 18° C. and 100° C. are shown by 
the broken lines to the right. The lines for the same material in the two cases are 
joined by a dotted line or by a bracket. 
As the electrical resistivity of a metal is nearly proportional to the absolute 
temperature, i.e., the electrical conductivity multiplied by the absolute temperature 
nearly a constant, and as this product is required in the discussion which follows, a 
table of values of the quantity at a number of temperatures within the range covered 
by the experiments is given on p. 437. It has been calculated from the values of the 
resistances taken from the curves of Plate 30. 
Discussion of the Electrical Results. 
A comparison of the values of the electrical resistivities obtained in the present 
experiments with those obtained at 18° C. and 100° C. by Jager and Diesselhorst, 
shows that the agreement is not quite so good as in the case of the thermal 
measurements. This is not likely to be due to errors of observation, as the electrical 
measurements admit of greater accuracy than the thermal. It seems rather to point 
to the greater influence on the electrical properties than on the thermal, of small 
differences in chemical composition, or in physical structure. This is in keeping with 
the results obtained by Gruneisen # in the cases of copper and iron. 
The influence of impurity on the electrical resistivities of metals is, in fact, so 
marked, particularly at low temperatures,! that a comparison of the resistivities found 
in the present experiments with those found by Dewar and Fleming (D.F.), and by 
Kamerlingh Onnes and Clay (O.C.), will serve as a test of the degree of purity of the 
materials used. 
* Gruneisen, ‘Ann. der Phys.,’ 3, p. 43 (1900). 
T Matthiessen, ‘Ann. der Phys.,’ 122, pp. 19, 68 (1864). Dewar and Fleming, ‘Phil. Mag.,’ 36, 
p. 271, (1893); Fleming, ‘Proc. Roy. Inst.,’ June, 1896, p. 9. Kamerlingh Onnes and Clay, ‘Comm. 
Leiden,’ No. 99 c (1907). 
