218 Mr. G. T. Beilby. Surface Flow in Crystalline, [May 23, 



" Surface Flow in Crystalline Solids under Mechanical Disturb- 

 ance." By G. T. BEILBY. Communicated by F. H. NEVILLE, 

 F.K.S. Keceived in revised form May 23, Read June 18, 

 1903. 



[PLATES 9 and 10.] 



In a paper read before the British Association at Glasgow, in 1901, 

 and in a further paper communicated to the Royal Society in 

 February, 1902, I described certain observations on the surface 

 structure of metals and other solids. These observations went to 

 show thai the effect of mechanical treatment of metals by cutting 

 tools or by polishing agents is to produce a surface layer or film 

 whose structure and appearance are distinct from those of the undis- 

 turbed substance below. -This surface layer has no appearance of 

 crystalline structure, but it has a certain structure granular or scale- 

 like, which lends itself to the formation of smooth, rounded, or 

 flowing forms like those assumed by a viscous liquid. It was also 

 observed that the edges of a piece of ductile metal which has been 

 torn asunder, generally, if not invariably, present the same appearance 

 of viscous flow and of granular or scale-like structure. 



Mr. F. H. Neville having suggested that the appearance of granular 

 or spicular structure which is seen by oblique illumination might be 

 due to the presence on the metal surface of crystalline facets so minute 

 as to be themselves invisible but capable of producing spots of light 

 like fixed stars seen through a telescope, the apparent size of the spots 

 being solely determined by the aperture of the object glass, I arranged 

 to make a fresh series of observations, using an oil immersion lens of 

 the highest numerical aperture and illumination by normally reflected 

 rays. 



The result of these observations has been that under the more 

 exacting conditions, the general appearance of the surface suggests, 

 as strongly as ever, the flow of a viscous, semi-solid substance, while 

 nothing of the nature of crystalline facets has been detected. 



In speculum metal it was first noticed that the stages in the flow of 

 the surface layer during polishing could be definitely traced as it 

 spread over and across the ridges and feirrows of the crystalline metal 

 below; figs. 9, 10, 11, 12 show the formation of the surface layer 

 and its removal by solution. Speculum metal being an alloy, it was 

 felt that in this case the effects of flow might to some extent depend 

 on the presence of the eutectic in which the crystalline grains are 

 embedded. In order, therefore, to eliminate this possible complication 

 the same observations were repeated using a piece of pure crystalline 

 antimony. In this also the appearances of flow were unmistakable, 

 being even more marked than in speculum metal. 



