AND ITS APPLICATION TO MR. B. TOWER’S EXPERIMENTS. 
173 
of the curved lines (fig. 6), in which the areas included between each pair of curved 
lines is the same as in the dotted figure. In this case, as in Case 1, the distance QP 
will represent the motion at any point P, and the slope of the lines will represent the 
tangential forces in the fluid as if the lines were stretched elastic strings. It is at 
once seen from this that the fluid will be pulled towards the middle of CD by the 
viscosity as though by the stretched elastic lines, and hence that the pressure will be 
greatest at O and fall off towards the ends C and D, and would be approximately 
represented by the curve at the top of the figure. 
Fig. 6. 
Case 3. Parallel Surfaces approaching with Tangential Motion. —The lines repre¬ 
senting the motions in Cases 1 and 2 may be superimposed by adding the distances 
PQ in fig. 6 to the distances PN in fig. 5. 
The result will be as shown in fig. 7, in which the lines represent in the same way 
as before the motions and stresses in the fluid where the surfaces are approaching with 
tangential motion. 
Fig. 7. 
In this case the distribution of pressure over CD is nearly the same as in Case 2, 
and the mean tangential force will be the same as in Case 1. The distribution of the 
friction over CD will, however, be different. This is shown by the inclination of the 
curves at the points where they meet the surface. Thus on CD the slope is greater 
on the left and less on the right, which shows that the friction will be greater on the 
left and less on the right than in Case 1. On AB the slope is greater on the right 
and less on the left, as is also the friction. 
Case 4. Surfaces inclined with Tangential Movement only. —AB is in motion as in 
Case 1, and CD is inclined as in fig. 8. 
