CONDUCTIVITY OF SELENIUM CRYSTAL 
329 
AN ATTEMPT TO: DETECT A CHANGE IN THE HEAT 
conductivity op a selenium crystal 
WITH A CHANGE IN THE ■ 
ILLUMINATION. 
L. P. SIEG. 
Introduction . — Modern electron theories indicate that the 
electrical and thermal condnctivities of ^ood conductors should 
stand in very close agreement with each other. Qne of the first 
theoretical developments was that of Drude.'' While, perhaps, 
it will not be necessary to rewrite his formula here, we can at 
‘least state that he determined on purely theoretical grounds that 
the ratio of the thermal to the electrical conductivities for good 
‘conductors should be a function only of the absolute tempera- 
ture. This theoretical formula has had excellent verification in 
the work of Jaeger and Disselhorst,^ who worked with most of 
the common metals. It occurred to the writer that an interest- 
ing experiment could be performed with an isolated crystal of 
'Selenium in order to determine whether or not the action of light 
dowers its resistance to heat conduction in the same or any other 
measure, that it does in the case of the electrical resistance. 
Little hope was entertained of obtaining as great a change in 
the thermal as in the electrical conductivity on account of the 
high resistance of the selenium, but it was hoped' that there 
might be some small effect in this direction. In looking up the 
literature of the subject it was found that there was but one 
published paper, that by Bellati and Lussana,® who worked, not 
with a crystal, but with thin sheets of crystallized selenium. 
Their method was somewhat crude, but they reported that there 
was an increase in the thermal conductivity when the thin plaie 
Was exposed to sunlight of the same order of magnitude as the 
increase in the electrical conductivity. (See reference to the 
Beiblaetter) . 
Apparatus and Method of Olisefvation.-^^he, apparatus used 
is illustrated in diagram in figure 27. Heat is generated in the 
lAnn. d. Phys. 1, 566, 190(T ; sr 900.' 
^Preuss, Akad. Wiss. Bei*. :SitzuQg^bH“r. SB; 719, 1899, also Phys. Tech. 
Reich., Wass. Abh. 3, 269, 19.0(}. • ■ - T 
3Atti, del. R, Inst, Veji...(6) 5u 19„,.I8Z7. , Also. Ab§, Beib. , d,. Aiih, IT, -818, 
1887. ■ ■ 
