130 
DE. JOULE ON SOME THEEMO-DTXAMIC PEOPEETIES OF SOLIDS. 
coefficient for the diminution of the elastic force of steel by rise of temperature. I find 
for the theoretical result, in the case of compression, 
H= 
283 7 -1 
1390^ 1 ^ 2379 
and in the case of extension, 
283 —7 1 1 1 
^~l390^ T“ ^ 7500^-11 ^ -428“ 
0°-00403, 
the results being necessarily the same in both cases. The deficiency of the actual result 
is not great, and is on the side of the probable error, in consequence of the unaroidable 
loss of a portion of the thermal effect by conduction from the junction. 
126. Thus even in the above delicate case is the formula of Professor Thomso> com- 
pletely verified. The mathematical investigation of the thermo-elastic qualities of 
metals has enabled my illustrious friend to predict with certainty a whole class 
interesting phenomena. To him especially do we owe the important advance which has 
been recently made to a new era in the history of science, when the famous philoso- 
phical system of Bacon will be to a great extent superseded, and when, instead ot 
arriving at discovery by induction from experiment, we shall obtam our largest acces- 
sions of new facts by reasoning deductively from fundamental principles. 
