220 Mr. G. T. Beilby. Surface Flow in Crystalline [May 23 r 



solvent a pit was discovered in which the film appeared to be in process 

 of building up, fig. 6. It is difficult to believe that the flowing metal 

 could be carried across the pit from side to side without the help of 

 some support from below. It seems most probable that this support 

 has been provided by small granules or flakes scraped off at an earlier 

 stage, which had lodged in the pit filling it loosely up to the general 

 surface level. Granules or flakes have been noticed in polishing 

 speculum metal, and their lodgment in the deeper scratches on the 

 surface has been actually observed. Fig. 7 shows a surface across 

 which a very fine scratch with a needle has been made. On polishing 

 with emery across the line of the scratch the shavings of metal were 

 caught and heaped up in the deep furrow made by the point of the 

 needle. 



These observations on the polishing of antimony show plainly that 

 under certain conditions this brittle, crystalline metal can be spread 

 over an irregular surface so as to form a smooth vamish-like covering 

 by which all the asperities are smoothed and rounded into gently- 

 flowing curves. It is further seen that this surface layer or film when, 

 as in the pits of figs. 5 and 6, it is not in solid contact with the more 

 massive metal underneath, has a much diminished reflecting power. 

 This illustrates in a new way the fact which I have referred to in my 

 earlier papers, that metal films as they become reduced in thickness 

 show a diminished reflecting power, a corresponding increase of trans- 

 parence at the same time taking place. 



The pressure necessary to produce surface flow in antimony is very 

 slight. The specimen was rubbed back and forwards on the leather- 

 faced block by the pressure of the fore-finger. The seizing of the 

 metal surface by the rouged leather could be distinctly felt as the 

 specimen was passed over it, and was obviously more marked with 

 rouged than with unrouged leather. On a moderately flat surface the 

 seizing seems to take place uniformly all over the surface and not 

 merely at a few points at a time, so that each passage over the leather 

 changes the whole surface slightly. 



When glass is furrowed by fine emery and then polished across the 

 furrows appearances of flow similar to those seen in metals can be 

 detected. I have not yet succeeded in making photographs which 

 show this in a satisfactory way, but hope to do so soon. 



The extremely slight mechanical treatment which will suffice to cause 

 molecular movement and flow on the surface of a highly crystalline 

 substance is seen in a remarkable way in the behaviour of calc-spar. 



A crystal of Iceland spar was split so as to present a fresh smooth 

 face which had never been touched or rubbed in any way. A small 

 drop of very dilute hydrochloric acid (containing about 0*2 per cent. 

 HC1) was placed on this fresh face and after 10 to 15 seconds was 

 removed by touching the spot with a torn edge of soft filter paper. 



