210 SCIENCE PROGRESS 



is increased by cold-working, whilst subsequent annealing 

 produces reunion under the action of capillary forces, was 

 proposed as long ago as 1868 by Prof. G. Quincke, 1 who has 

 since modified his views and now assumes that every metal, 

 even when pure, has a heterogeneous foam structure 2 and that 

 the cell-walls, which are chemically different from their contents, 

 modify the influence of mechanical work in displacing the 

 lamellae. In other respects his explanation of the phenomena 

 is in agreement with that of Prof. Tammann. 



At the other extreme stands a remarkable hypothesis which 

 has been proposed recently as the outcome of important experi- 

 ments in the Geophysical Laboratory of Washington. 3 The 

 hypothesis is to the effect that the flow of metals is due to 

 an actual melting. It is true that increase of hydrostatic 

 pressure has the effect of raising the melting-point of all but 

 a very few metals but it is contended that pressure producing 

 flow must have an entirely different effect. It has in fact been 

 shown, on theoretical grounds, that pressure must always 

 lower the melting-point if it be applied in such a way as to 

 act only on the solid while the liquid is free to escape ; 4 the 

 conclusion has been verified in the case of ice. If the heat 

 of fusion and the density of a metal at its melting-point are 

 known, it is possible to calculate the pressure which would 

 be necessary to melt a metal at atmospheric temperature. This 

 has been done and although the numbers obtained are very 

 large, the author of the memoir does not regard them as 

 impossibly so. The order in which the metals appear in such 

 a list coincides exactly with that of their elastic properties, 

 showing that the relation between melting-point and elasticity 

 is a real one whether the actual form of relation proposed 

 be correct or not. It is difficult to picture the manner in which 

 such melting can take place. It is true that the pressure 

 between two portions of metal on opposite sides of a cleavage 

 plane may be very much greater than the average pressure 

 on the metal under stress but the pressures demanded are 

 very large (1760 atmospheres in the case of lead and 14,000 

 atmospheres in that of silver at 27 , for example) and it would 



1 Ber. Akad. Berlin, 1868, 132. 



2 Proc. Roy. Soc. 1906, 78 A 60. 



3 J. Johnston,/. Amer. Chem. Soc. 1912, 34, 788. 

 • J. H. Poynting, Phil. Mag. 1887 [v.], 12, 32. 



