AND ITS APPLICATION TO MR. B. TOWER’S EXPERIMENTS. 
175 
The pressure of the intervening film of fluid would cause a force tending to separate 
the surfaces. 
The mean line or resultant of this force would act through some point 0. 
This point 0 does not necessarily coincide with Pj the point of maximum pressure. 
For equilibrium of the surface AB, 0 will be in the line of the resultant external force 
urging the surfaces together, otherwise the surface ACD would change its inclination. 
The resultant pressure must also be equal to the resultant external force perpen¬ 
dicular to AB (neglecting the obliquity of CD). If the surfaces were free to 
approach the pressure would adjust itself to the load, for the nearer the surfaces the 
greater would be the friction and consequent pressure for the same velocity, so that 
the surfaces would approach until the pressure balanced the load. 
As the distance between the surfaces diminished 0 would change its position, and 
therefore, to prevent an alteration of inclination, the surface CD must be constrained 
so that it could not turn round. 
It is to be noticed that continuous lubrication between plane surfaces can only take 
place with continuous motion in one direction, which is the direction of continuous 
inclination of the surfaces. 
With reciprocating motion, in order that there may be continuous lubrication, the 
surfaces must be other than plane. 
15. Revolving Cylindrical Surface. 
When the moving surface AB is cylindrical and revolving about its axis, the general 
motion of the film will differ somewhat from what it is with flat surfaces. 
Case 5. Revolving Motion, CD flat and symmetrically placed. —The surface velocity 
of AB may be expressed by U as before. The curves of motion found by the same 
method as in the previous cases are shown in fig. 10. 
Fig. 10. 
The curves to the right of GH, the shortest distance between the surfaces, will 
have the same character as those in fig. 9 to the right of C, at which is also the shortest 
distance between the surfaces. 
