AND ITS APPLICATION TO MR. B. TOWER’S EXPERIMENTS. 
233 
smallness of the subsequent wear, and the variety of the conditions as to magnitude 
of load, speed, and direction of motion. 
That a brass in continuous use should preserve a circular section with a constant- 
radius requires either that there should be no wear at all, or that the wear at any 
point P should be proportional to sin (90° — POH). 
Experience shows that there is wear in ordinary practice, and even in Mr. Tower’s 
experiments there seems to have been some wear. In these experiments, however, 
there is every reason to suppose that the wear would have been approximately pro¬ 
portional to c sin (<£ 0 —#) = c sin (90° — POH), because this represents the approach of 
the brass to the journal within the mean distance a, for all points, except those at 
which it is negative; at these there would be no wear. So long then as the journal 
ran in one direction only, the wear would tend to preserve the radius and true circular 
form of that portion of the arc from C to F (fig. 17, p. 193), altering the radius at F, 
and enlarging it from F to D. On reversal, however, C and F change sides, and hence 
alternate motion in both directions would preserve the radius constant all over the 
brass. The experience emphasized by Mr. Tower that the journal after running for 
some time in one direction would not run at first in the other, strongly bears out this 
conclusion. Hence it follows that had the journal been continuously run in one 
direction the condition of lubrication, as shown by the distribution of oil pressure 
round the journal, would have been modified, the pressure falling between O and B 
on the on side of the journal, a conclusion which is borne out by the fact that in the 
experiments with brass No. 2, which was run for some time continuously in one 
direction, the pressure measured on the on side is somewhat below that calculated on 
the assumption of circular form, although the agreement is close for the other four 
points (see fig. 2, Plate 8). 
When the surfaces are completely separated by oil it is difficult to see what can 
cause wear. But there is generally metallic contact at starting, and hence abrasion, 
which will introduce metallic particles into the oil (blacken it) ; these particles will be 
more or less carried round and round, -causing wear and increasing the number of 
particles and the viscosity of the oil. Thus the rate of wear would depend on the 
impurities in the oil, the values of c, y and the velocity of the journal, and hence 
would render the greatest velocity at which the maximum load could be carried with 
a large value of c small. A conclusion which seems to be confirmed by Mr. Tower’s 
experiments at twenty revolutions per minute. 
In cases such as engine bearings the wear causes the radius of curvature of the 
brass continually to increase, and hence a and c must continually increase with wear. 
But in order to apply the theory to such cases the change in the direction of the 
load (or Uj and V x ) have to be taken into account. 
That the circumstances of Mr. Tower’s experiments are not those of ordinary 
practice, and hence that the particular equations deduced in order to apply the theory 
MDOCCLXXXVI. 2 H 
