242 PROFESSOR E. G. COKER ON 
In order to test the truth of this, several experiments were made on bars in tension, 
using a thermopile for measuring the cooling effect caused by the stress applied, and 
an extensometer to determine the strain. This latter was of the usual Unwin pattern, 
except that the metal distance-pieces were replaced by mahogany rods, previously soaked 
in paraflin wax;and suitably capped. This precaution renders negligible any error due 
to any slight changes of temperature, as the coefficient of expansion of mahogany is © 
extremely small. The steel bar quoted above, for which the correction factor for 
radiation and conduction had already been determined, may be quoted as an illustration. 
The load was applied as uniformly as possible in a Buckton testing machine at a uniform 
rate of 4000 pounds per minute, and the galvanometer and extensometer readings were 
taken at each interval of 1000 pounds. The following readings were obtained :— 
TABLE, V. 
orrected 
hee, Extensometer Observed Gane 
Time, seconds. Load, pounds. Reading. Galvanometer Reading. 
Reading. e=-0045. 
0 0 0 0 0 
16 1,000 iid 2°5 2°59 
30 2,000 200 5:0 5°34 
— 105 
44 3,000 305 8:0 8°79 
— 105 
60 4,000 410 10°5 11°92 
— 105 
75 5,000 520 13:3 15°54 
— 105 : 
91 6,000 625 16:3 19°60 
— 100 
7,000 725 18°3 
— 100 
120 8,000 825 20°5 26°04 
— 102 
9,000 927 22°8 
— 103 
150 10,000 1,030 25:0 33°44 
— 100 
11,000 1,130 26'8 
— 120 
180 12,000 1,250 28°7 40°32 
195 13,000 vine 30:0 43°16 
14.000 \ Went off scale at Galvanometler reading 
: 13,600 lbs. went off |scale 
Note.—Distance of scale from mirror of galvanometer= 6’ 114”. 
' 
The galvanometer used in all the experiments mentioned in this paper was provided 
with a coil of resistance 5°2 ohms, and having about 300 turns; the thermopile was — 
