PROCEEDINGS OF THE SOCIETY. 119 



Mr. Rousselet said these slides were some which he had selected from 

 Mr. Hilton's collection — they did not illustrate any special subject, but 

 were quite of a miscellaneous character. 



Mr. F. Rogers read his paper, " On the Microscopic Study of Strain 

 in Metals," the suljject being illustrated by photographs, and specimens 

 shown under Microscopes lent for the occasion by Messrs. Beck. 



The President said this was a subject which must be of great interest 

 to many of the Fellows ; he would not attempt to say anything himself, 

 but had no doubt that some of those present would wish to discuss the 

 paper. 



Mr. W. Rosenhain said that it was very difficult to discuss Mr. 

 Rogers' paper in that assembly, because it dealt with a special branch of 

 a highly technical subject, and he hoped that the results described in the 

 paper would be brought before an assembly of metallurgists, where they 

 could be adequately discussed. If, however, there were any amateurs 

 interested in the subject present, he would like to warn them that there 

 were one or two of Mr. Rogers' statements which, perhaps, required a 

 little care in their application. For instance, Mr. Rogers seemed to 

 consider it likely that such substances as pearlite did not possess a crys- 

 talline structure, and that, consequently, their behaviour under stress 

 was essentially different from that of crystalline metals. Of course it 

 was not easy to see what was the physical structure of some of these 

 bodies, more particularly of some of the transition products, but he 

 (Mr. Rosenhain) thought that there was some evidence for believing that 

 the structure of well-developed pearlite was crystalline ; the subject was, 

 however, one that required much further investigation. 



The whole question of the behaviour under various stresses of metals 

 consisting of two constituents of widely different mechanical properties, 

 was a very interesting, but also a very difficult one. Mr. Rogers had 

 studied the behaviour of such metals under alternating stresses, while 

 the speaker had studied their fracture under various other forms of 

 loading, and he would like to point out that the conclusions as to the 

 path of fracture in a heterogeneous metal of this kind, depended upon 

 the nature of the forces producing the fracture, the deciding factor being 

 the presence or absence of considerable deformation prior to actual frac- 

 ture. From this result one would expect Mr. Rogers' specimens to 

 show two types of fracture ; those portions of any specimen which had 

 broken first, while the specimen was stiff enough to resist any con- 

 siderable bending, would show the " cleavage type " of fracture, while 

 those portions of the fracture which broke last would show the effects of 

 sensible bending, which must begin as soon as the specimen iiad f ractm'ed 

 to a certain definite extent. 



Perhaps the most interesting portion of Mr. Rogers' work was that 

 dealing with the very beautiful application of heat-tinting, to the study 

 of these fractures which Mr. Rogers has introduced. The results 

 obtained in that way were most valuable, but he supposed that only 

 those fissures were represented by tinted areas on the broken specimen 



