442 • PROFESSOR C. H. LEES: THERMAL AND ELECTRICAL 
The curves show that there is a tendency for the values of the conductivity 
constant JcjKt to collect in the neighbourhood of the value 2'4x 10 -8 , within the range 
given by the electronic theories, and that this tendency is rather more marked in the 
values calculated from Jager and Diesselhoest’s results than in those calculated 
from the present experiments. Lead, tin, and possibly cadmium give values 
independent of temperature over the wide range covered, and therefore support the 
statement made bv L. Lorenz in 1882. Zinc, silver, copper and aluminium show 
a marked decrease of the constant as the temperature decreases. Nickel, steel, and 
possibly iron, show an increase as the temperature decreases. This appears to be the 
characteristic behaviour of alloys. The values for aluminium and copper are 
decidedly below, while those for nickel and iron are decidedly above, the value 2* * * § 4. 
All the alloys give values above this, and, with the exception of brass, decidedly 
above. This large value of the constant for alloys especially at low temperatures 
is in keeping with and extends the results obtained previously by Gruneisen,* who 
found that increase of impurity in copper and iron at ordinary temperatures increased 
the value of the constant. 
It is necessary to bear this increase in mind in basing any argument on the values 
observed. The high values for nickel and iron may, since both contained a little 
impurity (about 1 per cent.), be ascribed to the impurity. In the cases of the 
other metals, with the exception of aluminium, which contained a little impurity 
(about 1 per cent.), it is not probable that any small amount of impurity present in 
them could have materially influenced the positions of the curves. In the case of 
aluminium it seems possible that the curve at low temperatures may be a little high, 
owing to the small quantity of impurity present in the metal. 
The only conclusion which can be drawn from the curves seems to be that the 
Lorenz law of constancy of the value of I'/kI at different temperatures for each metal 
has only a restricted application, and that although the metals which support the law 
give nearly the same value, 2'4, for the constant,! the other metals have values of 
the constant which differ from 2’4 by amounts far outside the limits of experimental 
error. | 
These facts are not of such a character as to provide strong support for any of the 
electronic theories mentioned on p. 439 in their present forms. 
A modified t heory has been put forward recently by Professor J. J. Thomson § to 
get over a difficulty he pointed out in the older theories, which made the energy 
* E. Gruneisen, ‘Ann. der Rhys.,’ 3, p. 43 (1900). 
t It is worthy of note that for mixtures of these metals, Matthiessen, ‘Ann. der Phys.,’ 110, p. 190 
(I860), found that the electrical conductivities, and Schulze, ‘ Ann. der Phys.,’ 9, p. 555 (1902), that the 
thermal conductivities, could he calculated from the relative volumes of the constituents present. 
[1 Note-added June 1.—The variations of the values of k/xt for the same metals at higher temperatures 
will form the subject of a future communication.] 
§ J. J. Thomson, ‘ Journ. Inst. Elect. Eng.,’ 38, p. 455 (1907), or ‘Corpuscular Theory of Matter,’ p. 86. 
