1917] A SIMPLE PROBLEM IN FORCED LUBRICATION 517
In practice the diminution of h calls for the utmost accuracy in fitting together the two opposed surfaces, which, however, need not be accurately plane, as well as the removal of all suspended solid matter from the lubricant.
When this is attended to, there should be no wear of the solid surfaces, which should never come into contact. To attain this ideal it is evidently necessary that the feed of lubricant should be established before the rotation commences.
It should be observed that no property of oil beyond viscosity is involved, and that the investigation may be expected to remain valid until the thickness (Ji) of the layer is approaching molecular limits.
P.S.—I may perhaps mention that I have made a small model, in which the opposed surfaces are those of two pennies ground to a fit, and the " lubricant " is water supplied from a tap.In practice r0 would have to be finite though small, and would correspond to the radius of the perforation in the lower fixed plate, not much disturbing (11). In fact, if jp0 be the pressure of the feed corresponding to r0,