GGQ TRANSACTIONS OF SECTION G. 



the practical woric of mgiQccring relies. TLe man whose daily business leads biiu 

 through familiar tracks in a forest does well to stray from time to time into the 

 shady depths that lie on either hand. The eyes of his imagination will be opened. 

 He will at least learn his own limitations, and, if he is fortunate, he may gain some 

 clearing on a hilltop which commands a wider view than he has ever had before. 



The following Paper was read : — 



Modern Armour and its Attack.^ By Major W. E. Edwards, E.A. 



FRIDAY, AUGUST 3. 



The following Papers were read : — 



1. The Removal of Dust and Smoke from Chimney Gases.'^ 

 By S. H. Davies and F. G. Fryer. J 



2. Standardisation in British Engineering Practice. 

 By Sir John Wolfe-Barry, K.C.B., F.B.S.—See Reports, p. 339. 



3. The Deformation and Fracture of Iron and Steel. 

 By Walter Rosenhain. 



The object of the author was to illustrate the manner in which microscopic 

 examination is able to throw fresh light on the physical behaviour of metals 

 under the action of stresses above the elastic limit ; the researches of Professor 

 Ewing and the author on this subject were referred to, and the general conclusions 

 arrived at in those researches were recapitulated, and the most characteristic 

 features of ' slip-bauds ' were described. Reference was then made to the 

 divergent views and observations of Osmond, and the author's interpretation of 

 these observations was given, especially in reference to the appearance of slip- 

 bands under oblique light, evidence of the author's view being shown by the aid 

 of multi-colour illumination reproduced by a process of colour-photography. The 

 author then referred to the theory of the hard and soft states in metals advanced 

 by Beilby, and, while largely accepting Reilby's ideas, emphasised the importance 

 of the state of temporary mobility which mechanical disturbance confers upon 

 layers of molecules on or near the surfaces of slip; by the aid of this view the 

 author advanced an explanation of the state of semi-plasticity which follows upon 

 over-strain in iron and steel, and also of the process of the recovery of elasticity 

 which follows upon this condition ; microscopic evidence in favour of this view 

 being given. The next section of the paper dealt with the phenomena attending 

 plastic deformation in an alloy of iron, nickel, manganese and carbon, discovered 

 by Carpenter, Hadfield and Longmuir (' alloy K ') ; the author advanced the view, 

 based upon microscopic evidence, that the change of constitution is confined to the 

 surfaces of slip or to twin lamellae. 



The following portions of the paper described the method of studying the 

 microscopic surface configuration of specimens of metal by means of trans\'erse 

 sections obtained after the specimen has beeu embedded in a mass of electro- 

 lytically deposited copper or other metal ; the applications of this method to the 

 study of slip-bands were first described, photo-micrographs of slip-bands in 



' Published in Engineer, September 7 and 14, 1906. 

 - Published in the Electrical Bevieiv, August 10, 1906. 



