264 



NA TURE 



[March 2, 1922 



mind to conceive the ad infinitum refining of scratches 

 to the attainment of a perfect sheen. But in actual 

 practice, with a last abrasive even so fine as particles 

 of rouge, it seemed as if there must somehow be a 

 jump at the end between these earthy scratches and 

 the perfect polish of speculum or plate glass., The 

 practical attainment of such a polish seemed much 



Fig. 3. — Etched calcite surface showing the untouched skin and the 

 under surface at 500 and 1000 ^/n. From " Aggregation and Flow 

 of Solids." 



more easily understood when a custodian of some of 

 the finest old silver at Cambridge, on being asked how 

 the brilliance was produced, simply exhibited the flesh 

 side of an ample thumb, with a gesture and mien 

 indicative of a flattening pressure exerted steadily 

 through the ages. Sir George Beilby now tells us, 

 and it is a relief to know it, that the microscopically 

 differentiable particles of rouge are smaller than we 

 thought, that they are also much harder, and that 

 when they are spread over a leather they present a 

 layer such that when the leather is passed over the 

 glass or metal surface, this is seized as a whole, the 

 mobility of a hquid is temporarily produced, and 

 when the leather has passed, a film is left with all 

 the qualities of matter that has set like melted glass. 

 Not only so, but " whilst to produce ' mass flow ' in 

 the hardened steel of which a razor is made a differential 

 pressyre of hundreds of tons per square inch would 

 be required, yet the ' surface flow ' necessary to keep 

 the edge of the razor in perfect cutting condition can 

 be effected by hghtly stropping the blade on the bare 

 hand a few times daily, before and after use ! " 



These examples are perhaps sufficient to indicate 

 why and how this work on the surface leads to a 

 study of the hard and soft state in metals, the flow of 

 rocks and ice, the phosphorescence and tribolumin- 

 escence of solids, and many other things besides. 



A word must be said about the magnitudes dealt | 

 NO. 2731, VOL. 109] 



with in the investigations. The study of a calcite 

 surface will suffice as an illustration : — 



" When a condensed beam of sunlight was used 

 to give oblique illumination of the surface, it was 

 possible to detect the effect of a drop of acid which 

 contained only o'oooi25 per cent of HCl. The depth 

 of the layer removed did not exceed 0*62 /a/x. . . . 

 If it is correct to assume that the solvent effect of the 

 acid was uniformly distributed over the whole surface 

 of the pit, then it follows that a roughening of the 

 surface not more than two molecules in depth has 

 been detected." Again, " the mechanical disturbance 

 caused [on calcite] by the poHshing agent penetrates 

 to a depth of 500 to 1000 /a/x." 



The frame of reference of Sir George Beilby's think- 

 ing has been almost wholly that which preceded sub- 

 atomism. In a short chapter he sketches his tentative 

 working hypothesis of molecular " pulsation cells." 

 Of this it must suffice to say that it has clearly served 

 its purpose, for it has worked — it has led to a solid 

 output of new knowledge. " Cohesion " is isolated 

 in the old way as a force sui generis, and a fine picture 

 is made of cohesion holding matter together in a dead 

 world until there comes the advent of heat " like the 

 first breath of approaching spring into the sleeping 

 buds." Sir George Beilby has brought his rich gift 

 of facts up to the frontiers of the newer physical 



Fig. 4. — Microscopic crystal of antimony. From "Aggregation and 

 Flow of Solids." 



science. It must obviously engage the interest of 

 those on the other side. There are especially to be 

 mentioned the Braggs, the work and views of Lang- 

 muir, and the new light on lubrication coming from 

 W. B. Hardy's experiments. But whatever may be 

 added, the facts remain as a remarkable addition to 

 scientific knowledge. 



In conclusion, one or two suggestions may be made. 



