214 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
Then with these assumptions in mind : 
Q= Kl(e ^~ e? )— 1 1 = K * (e? ~ ei) At where the symbols are defined as 
follows : 
e 3 = temp, of upper surface of disk a. 
e 2 = “ “ lower “ “ “ 
= “ “ upper “ “ “ b. 
ei' = ■ “ “ lower “ “ “ 
K x = thermal conductivity of disk a. 
K 2 = “ ‘ ' “ “ b. 
di — thickness of disk a. 
d 2 = thickness of disk b. 
From the above equation we deduce at once : 
_ d_ 8 (e 3 — e 2 ) 
K x ” d,. (e 2 — ej 
Fig. 32. Arrangement ot apparatus for experiment. 
Figure 32 is a diagram of the apparatus used. The guard 
ring to prevent end losses is clearly shown. The temperatures 
e 3 , e 2 , and e x were obtained by means of thermo-couples embedded 
in copper disks with insulated guard rings of the same material 
and thickness. They were made very thin and copper being a 
far better conductor of heat than the lead or tellurium the effect 
was found to be negligible. One of these was placed above disk 
a, a second between disk a and disk b, and a third below disk 
