AND ITS APPLICATION TO MR. B. TOWER'S EXPERIMENTS. 
213 
As B expresses the rate at which the heat generated in the oil film is carried away by 
conduction through the oil and the surrounding metal, any estimate of its value is very 
difficult. If we could measure the temperature at the surfaces of the metal, B might 
be made to depend only on the thickness and conductivity of the oil film. But before 
heat can escape from the journal or bearing it must pass along intricate metal channels 
formed by the journal or shaft and its supports ; and, on consideration, it appears that 
in ordinary cases the resistance of such channels would be much greater than the 
resistance of the oil film itself. For example, in the case of a railway axle, the heat 
generated must escape either along the journal to the nearest wheel or through the 
brass and the cast-iron axle box to the outside surface, so that either way it must 
traverse at least three or four inches of iron. This is about the best arranged class of 
journals for cooling. In most other cases heat has much further to go before it can 
escape. However, in every case B will depend on the surrounding conditions and can 
only be determined by experiment. From the experiments, to be considered in the 
next section, it appears that 
B = 1 (about) . . .(123) 
But it is to be noticed that Mr. Tower has introduced a somewhat abnormal con¬ 
dition by heating the oil bath above the surrounding temperature. For in this way, 
letting alone the heat generated by friction, there must have been a continual flow of 
heat from the bath along the journal to the machinery ; and, considering the compara¬ 
tively limited surface of the journal in contact with the hot oil and the large area of 
section of the journal, it appears unlikely that the temperature of the journal was 
raised by the bath to anything like the full temperature of the latter, a conclusion 
which is borne out by Mr. Tower’s experiments with different temperatures in the 
bath (Table XII., Art. 34), which shows that the temperature of the bath produced a 
much smaller effect on the friction than would have followed from the known viscosity 
of oil had the temperature of the oil film corresponded with the temperature of the 
bath. 
Thus the temperature of the film independent of friction is not the temperature of 
the bath or surrounding objects, and as it is unknown until determined from the 
experiments, it will be designated as 
T,, 
and the suffix x used to designate the particular value for T=T„ of all those quantities 
which depend on the temperature as 
He n.c 
If T be the mean temperature of the film, 
T-T,=T,. (123a) 
where T m is the rise of temperature due to the film. 
