250 THE MEASUREMENT OF STRESS BY THERMAL METHODS. 
CoNCLUSION. 
The application of the thermopile to determine the thermal change in a body, and} 
hence the intensity of the stress, has an extremely wide application, since the thermo-— 
elastic equations deduced by Lord Ketvin are generally applicable to elastic bodies - 
subjected to every type of stress. Only a limited number of cases have been treated in 7 
the preceding pages, chiefly with a view of showing the range of application of the 
method. The thermopile, while probably forming the most convenient method of — 
determining the thermal state of a body under stress, is not the only one which could | 
be applied. Durmg the summer of 1903, the author, by the kindness of Professor Cox, — 
Director of the Physics Building, M‘Gill University, was enabled to experiment with a 
Boys radio-micrometer, which was set up in close proximity to specimens in tension and 
compression, and the readings were found to be proportional to the load; but, with the 
limited experience of the author, it was found to be much less convenient than a thermo- 
pile, mainly because of the extreme delicacy of the apparatus, and the dithculty of 
setting it horizontally upon a steady base near the testing machine. 3 
In conclusion, the author desires to express his warmest thanks to Professor Bovey, 
F.B.S8., for the use of his well-equipped testing laboratory, and to Professor RuTHER- 
FORD, F.R.S., for valuable suggestions during the progress of the work; also to Mr 
M‘Kerrcow, Demonstrator in Civil Engineering, for his untiring assistance in making 
observations. | 
