614 president's address-— .sectiox h 



the best it means that he best makes use of the accumulated experi- 

 ence and deductions from experience of the great men who have gone 

 before. No man can become an engineer by the mere reading oi 

 booiis, and, on the other hand, no engineer can become a master of 

 his profession without reading. In this way, he may build his own 

 little mound of experience on top of the hill that has been laboriously 

 built by his predecessors, and so by commanding a wider view than 

 they have had he may perchance see possible avenues of progress 

 hidden from them. Engineering progress depends upon both theory 

 and practice marching forward together, and every engineer is bound 

 to welcome any illuminating light tlu'own upon his efforts, no matter 

 from what direction it comes. 



In spite of the great numbers of investigations into the be- 

 haviour of materials under stress that have emanated of late years 

 from the numerous well-equipped engineei-ing laboratories all over 

 the world, comparatively small progress has been made towards any 

 real understanding of the nature of the phenomena observed. 

 Inunense numbers of observations have been made upon the breaking 

 strength, the yield point, the amount of elongation imder stress of 

 various materials, upon the fatigue of metals under alternating or 

 intermittent stresses, the flow of metals under stress, methods of 

 hardening and softening, and the effect of changes of temperature 

 i!;;on strength and elasticity, but, although there must necessarily be 

 an intimate connection between these various phenomena, it is only 

 comparatively recently that any attempt has been possible to picture 

 the nature of the processes taking place. I should think that most 

 men who have done much in the way of experimenting upon the 

 behaviour of iron and steel in the testing laboratory have been im- 

 pressed with the unsatisfactory nature of the task of tabulating 

 columns of experimental results with no real guiding principle by 

 "which they can be co-oixlinated. Of course it may be said from a 

 purely practical point of view that so long as we know the strength 

 and elasticity of a piece of iron, that is all the engineer w^ants to 

 know for structural purposes, and that the nature of the molecular 

 processes is not his concern. But the history of engineering is full 

 of examples of the practical advantages that may be derived by 

 the engineer from a scientific enquiry into the phenomena with which 

 he has to deal, and we cannot divorce the practice of engineering 

 from its philosophy. In the case before us it is obvious that any 

 theoiy which will throw light upon the nature of the molecular 

 processes that lead up to the fracture of a metal, enabling us to 

 form some sort of mental picture of what happens in the coi'related 

 phenomena of yield point, fatigue, and elasticity, or to elucidate the 

 pioblems of annealing and tempering, may be a very important aid 

 to progress, even if, as is most })robable, the theory be only partially 

 correct. The attempts that have been made in this direction have 

 been largely due to the progress in the study of the metals by the aid 

 of the microscope, an instrument that we are apt to associate rather 

 with the study of butterflies than with engineering. But by its aid 

 such light has been thrown upon the structure of metals that it is 

 not at all unlikely that the microscope will in the future form just 

 as essential a feature in the engineering laboratoiy as the testing 

 machine. 



