

of Cavitation in Lubrication. 333 
seen to have moved slightly to the right hand. Following 
it is seen a dark line behind which is a broader light space 
traversed horizontally by small streaks of dark liquid. This 
broader light space is filled only with the vapour: of the 
liquid, for, as we have already stated, it is completely filled 
with dark liquid as soon as the motion ceases. This cavity 
has been formed by the splitting of the liquid, and it is of 
special interest to notice that it is formed not immediately 
at the line of nearest approach but some short distance 
behind this line. That the greatest tension in a lubricating 
liquid is not at the point of nearest approach of the surfaces 
was shown theoretically by Reynolds, who calculated the 
pressures and tensions in a layer such as this. Fig. 5 is 
Fig. 5, 
PRESSURE 



TENSION 
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taken from Reynolds’ paper, and from it we see that the 
point of maximum tension is behind the point of nearest 
approach. 
§ 7. In figs. 6 and 7 (PI. XVIII.) is represented a lens lying 
on a plane surface. In fig. 6 everything is at rest, and the 
light spot at the centre shows the point of nearest approach of 
the lens to the plane. In fig. 7 the lens is being rolled from 
left to right by the fingers and a collection of cavities has been 
formed behind the point of nearest approach. As with the 
cylindrical surface, on stopping the motion the cavities fill 
completely. 
Phil. Mag. 8, 6. Vol. 7,.No. 40. April 1904. 2A 
