486 
MR. C. H. LEES ON THE THERMAL CONDUCTIVITIES 
surfaces of these cups were amalgamated so as to make good contact with the iron bar. 
The insides of the cups were amalgamated, and each cup contained sufficient mercury 
to fill it entirely when the thermometer was placed in it. At opposite extremities of 
a diameter, about half way down each cup, two small holes, like those in the divided 
bar were punched, and into these holes, which were amalgamated, the wires of the 
thermo-couple could be inserted. The constants of the couple are in this way deter¬ 
mined under exactly the same conditions as when they are in use. The iron bar was 
buried in sawdust, and the copper mercury cups placed in such positions on the 
upper surface that the thermometer read in them 90° C. and 55° C. respectively. 
After the insertion of the wires of the thermo-couple into the holes of the mercury 
cups, the cups were surrounded with sawdust, and 10 minutes allowed for the tem¬ 
perature of the cups to get as nearly as possible uniform before observations were 
taken. 
In an experiment made in the early part of the work the following observations 
were taken :— 
(a) Temperature of hot junction, 85°'90 C. 
Temperature of cold junction, 15 0, 67. 
Deflection of galvanometer in scale divisions, 296. 
Resistance of circuit, mean of observations taken, as previously described 
1-431 ohm. 
E.M.F. of element in units used, 423’6. 
( b ) Temperature of hot junction, 55 o, 60. 
Temperature of cold junction, 15 0, 74. 
Deflection of galvanometer, 162"3. 
Resistance of circuit, 1'448 ohms. 
E.M.F. of element in units used, 235-0. 
These observations are sufficient to determine the constants in the formula 
e = a(t 2 — h) (1 + b t 2 + t x ) where t 2 and t 1 are the temperatures of the hot and 
cold junctions respectively. It was found more convenient for the reduction of 
observed E.M.F.’s to temperature, to draw up a small table of values of a (1 + b t 2 + t x ) 
for different values of t 2 -fi t v Thus, for the above observations, w r e have :— 
h ~t h- 
a (1 + 6 L + ij). 
Differences. 
101 
6-030 
+ 2 
+ -009 
91 
5-985 
4 
•018 
81 
5-940 
6 
•027 
71 
5-895 
8 
•036 
61 
5-850 
51 
5-805 
41 
5-760 
31 
5-715 
