

of Cavitation in Lubrication. ook 
paper and transmitted through the system, all the appearances 
which are here described may be seen. It is also very con- 
venient for photographing etfects. 
§ 4. When the rolling ceases it has been remarked that 
the cavity fills up quickly with mobile, and slowly with 
viscous liquids, and this filling of the cavity is quite com- 
plete unless some gas or air has found its way in. The 
liquid is forced back to fill the vacuous space by the atmo- 
spheric pressure, and the rate of filling is decided by the 
viscosity of the liquid. That it is so is seen by the slowness 
with which oil or glycerine fills the cavity made in it, and is 
also evident from the reiatively large size of the cavity 
formed in these liquids. The cavity which is formed must 
be produced either by splitting the liquid itself or by tearing 
the liquid from the glass surface. ‘The effect may be de- 
scribed as a case of “cavitation.” This word has been used 
by the Hon. C. A. Parsons (‘ Nature,? May 1898) to describe 
the production of a cavity in water bya very rapidly rotating 
screw-propeller. In his experiment the atmospheric pressure 
was removed from the surface of the water by an air- 
- pump. 
§ 5. Before describing the actual effects some account of 
the stresses in the liquid will help to make the conditions of 
the cavitation more clear; and in this we shall follow the 
graphical method used by Osborne Reynolds in his paper 
on the “Theory of Lubrication” (Phil. Trans. A. 1886). 
In this paper the origin of the force resisting the motion of 
two surfaces separated by a continuous and copious supply 
of lubricant is discussed, and it is shown that it is wholly 
accounted for by the viscosity in the lubricant. 
Let AB and CD represent the sections of two parallel 
solid surfaces, extended ‘infinitely at right-angles to the 
Fig. 1. 
CW, LLL D 
E R F 
G nme H } 
A PF Le B 
ITITVTTTITTT QTV GIIT?: TMT 
—— > 
paper, and between them let us suppose three fluid layers 
lie, bounded by the lines EF and GH. Let us suppose the 
viscosity of the layers in contact with the solid walls is the: 
