268. Mr. G. T. Beilby on the Hard 
directly imparted to them by the movement of one portion of 
the substance over another. 
44, The two kinds of mobility, M and M’ in the trans- 
formations 0 '——= M-—>-A and A——> WM’ — = Ga 
be compared to the two ways in which the hands of a watch 
may be moved. In the M’ phase the movement of the hands 
is due to the internal energy of the watch which is centred 
in the coiled spring ; in the M phase the movement is im- 
posed on the hands from without by the turning of the 
setting spindle. 
45. The existence of mobility in the transformation from 
hard to soft through M’ falls perfectly in line with the phase 
transformations which have been studied by metallurgists for 
many years past. Barus suggested that ‘‘ when iron passes 
through the temperature ot recalescence its molecular con- 
dition is for an instant almost chaotic.” * Roberts-Austin, 
referring to the case of a glass-hard steel rod suddenly 
exposed to a temperature of 300°, says ‘‘that if all the molecules 
passed from Osmond’s « state to his @ state together, the steel 
would necessarily be a liquid.” 
46. The existence of a mobile phase of an entirely new 
kind has been brought to light and rendered practically 
certain by the microscopic observations to which I have 
referred. A further observation ofa very singular kind which 
bears directly on this subject is detailed later in par. 71. 
Some Applications of the Phase Theory of Flow. 
47. The observations of Ewing and Rosenhain on the 
crystalline structure of metals and the deformation of that 
structure by overstrain t+ have demonstrated the important part 
which is played by crystalline deformation in masses of metal. 
They have shown that it is possible with the microscope to 
trace the rougher mechanism of the deformation as it takes 
place by successive slips of the lamellze of which the crystalline 
grains are composed. The phase theory now supplies what was 
needed for a more intimate explanation of the changes which 
occur at the gliding surfaces. My observations on surface-How 
have shown how slight is the force required to break down the 
crystalline into the amorphous phase ata surface. Itis therefore 
evident that the lamella cannot slip over each other without 
there being formed between them an exceedingly thin mobile 
layer which immediately passes on into the hardened phase. 
By the slipping over each other of grains, of lamelle, and of 
* “Nature,” vol. xii. p. 369 (1890); ‘Introduction to the Study of 
Metallurgy,’ p. 170 (1902). 
+ Phil. Trans. Roy. Soc., A. vol. excill. pp. 853-377. 
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