184 
PROFESSOR 0. REYNOLDS ON THE THEORY OF LUBRICATION 
escaping into broader spaces, allow the brass to approach and eventually to touch the 
journal at the narrowest spaces, and this would be particularly the case near the ends. 
As a matter of fact, the general fit of two new surfaces can only be approximate ; 
and how near the approximation is, is a matter of the time and skill spent on preparing, 
or, as it is called, bedding them. Such bedding as brasses are subject to would not 
bring them to a condition in which the hills and hollows differed by less than a t o o o o th 
part of an inch, so that two such surfaces touching each other on the hills would have 
spaces as great as a yygyth of an inch between ,them. This seems a small matter, but 
not when compared with the mean width of the interval between the brass and the 
journal which, as will be subsequently shown, was less than °f an inch. 
It may be assumed, therefore, that such inequalities generally exist in the surfaces 
of new brasses and journals. And as the surfaces according to their material and 
manner of support yield to pressure the brass will close on the journal at its ends, 
where, owing to the escape of oil, there is no pressure to keep them separate. 
Fig. 16. 
The section of a new brass and journal taken at GH will therefore be, if 
sufficiently magnified, as shown in fig. 16, the thickness of the film, instead of 
being, say, of TlToootl 18 °f an inch, varies from 0 to Tooo oths, and is less at the ends 
than at the middle. 
In this condition the wear will be at the points of contact, which will be in the 
neighbourhood of GH on the off side of 0 (fig. 13), so that if the journal runs in one 
direction only the surfaces in the neighbourhood of GH (on the off side) will be 
gradually worn to a fit, during which wear the friction will be great and attended 
with heating, more or less, according to the rate of wear and the obstruction to the 
escape of heat. 
So long, however, as the journal runs in one direction only GH will be on one side 
(the off side) of 0, and the wear will be altogether or mainly on this side, according 
to the distance of H from 0. 
In the meantime the brass on the on side is not similarly worn, so that if the 
motion of the journal is reversed and the point H transferred to the late on side the 
wear will have to be gone through again. 
That this is the true explanation is confirmed if, as seems from Mr. Tower’s report, 
the heating effect on first reversing the journal was much more evident in the case of 
the oil bath. 
