496 Professor H. C. H. Carpenter [March 7, 



ticular field of knowledge are not as a rule due to workers in that 

 field, but to those whose labours apparently have little direct relation 

 to them. In this case I refer to the researches of Sir George Beilby 

 on the hard and soft states in metals. Those researches were carried 

 out on metals which could be obtained in a very high degree of 

 purity, and which did not possess, so far as is known, any critical 

 points, such as those that characterize tlie metal iron. 



The experiments were carried out for the most part with gold, 

 silver and copper, and there is no doubt that he made a wise choice 

 in selecting tbese particular materials, which are most suitable for 

 the particular study which he had in view. His early researches 

 were concerned w-ith the microscopic study of the structure and 

 behaviour of thin films of metal, and this led him to the discovery 

 of the nature of the operation of polishing, etc. He found that in 

 this operation a true skin is formed over the polished surface, and that 

 this gives unmistakable signs that it has passed through a state in which 

 it must have possessed the perfect mobility of a liquid, although the 

 operations were carried out at the ordinary temperature, which is several 

 hundred degrees below the melting-points of the metals in question. 



The metal itself in the annealed condition is composed of crystals, 

 but the skin formed in grinding and polishing possesses distinctive 

 qualities which differentiate its substance very clearly from that of 

 the unaltered substance beneath it. It is for instance much harder, 

 and even when formed on the face of a crystal on which the hardness 

 varies in different directions, its hardness is the same in all directions. 

 Since the skin can be dissolved off in stages, it was possible thus to 

 gain an insight into the history of its formation. The surface skin 

 can thus be investigated analytically as w^ell as synthetically ; it can 

 be built up in stages by polishing, and it can equally easily be 

 removed in stages ; the latter operation having the advantage over 

 the former that the method of solution lends itself to a step by step 

 removal of great refinement and accuracy. The discovery that layers 

 of a solid many hundreds of molecules in thickness can have the 

 mobility of the liquid state conferred upon them by purely mechani- 

 cal movement, opened up a new field of inquiry into the internal 

 structure of metals which have been hardened by cold working. As 

 a result of this inquiry, Sir- George Beilby put forward a theory 

 of the hard and soft states of metals, according to w^hich hardening 

 results from the formation at all the internal surfaces of slip or 

 shear of mobile layers similar to those produced on the outer surface 

 by polishing. These layers only retain their mobility for a very brief 

 period, and then solidify in a vitreous amorphous state, thus forming a 

 cementing material at all surfaces of slip or shear throughout the mass. 

 The keystone of the theory is thus the instant liquefaction followed by 

 the solidification of sheets of molecules during mechanical deformation. 



It was never found possible, even by the severest deformation, to 

 convert a crystalline into a completely amorphous metal. The 



