AND ITS APPLICATION TO MR. B. TOWER’S EXPERIMENTS. 
159 
Section I. —Introductory. 
1. Lubrication, or the action of oils and other viscous fluids to diminish friction 
and wear between solid surfaces, does not appear to have hitherto formed a subject for 
theoretical treatment. Such treatment may have been prevented by the obscurity of 
the physical actions involved, which belong to a class as yet but little known, namely, 
the boundary or surface actions of fluids ; but the absence of such treatment has also 
been owing to the want of any general laws discovered by experiment. 
The subject is of such fundamental importance in practical mechanics, and the 
opportunities for observation are so frequent, that it may well be a matter of surprise 
that any general laws should have for so long escaped detection. 
Besides the general experience obtained, the friction of lubricated surfaces has been 
the subject of much experimental investigation by able and careful experimenters. 
But, although in many cases empirical laws have been propounded, these fail for the 
most part to agree with each other and with the more general experience. 
2. The most recent investigation is that of Mr. Beauchamp Tower, undertaken at 
the instance of the Institution of Mechanical Engineers. Mr. Tower’s first report 
was published November, 1883, and his second report in 1884 (“Proc. Inst. Mechanical 
Engineers ”). 
In these reports Mr. Tower, making no attempt to formulate, states the results of 
experiments apparently conducted with extreme care and under very various and 
well-chosen circumstances. Those results which were obtained under the ordinary 
conditions of lubrication so far agree with the results of previous investigators as to 
show a want of any regularity. But one of the causes of this want of regularity, 
irregularity in the supply of the lubricant, appears to have occurred to Mr. Tower 
early in his investigation, and led him to include amongst his experiments the unusual 
circumstances of surfaces completely immersed in oil. This was very fortunate, for 
not only do the results so obtained show a great degree of regularity, but while 
making these experiments he was accidentally led to observe a phenomenon which, 
taken with the results of his experiments, amounts to a crucial proof that in these 
experiments with the oil bath the surfaces were completely and continuously sepa¬ 
rated by a film of oil; this film being maintained by the motion of the journal, 
although the pressure in the oil at the crown of the bearing was shown by actual 
measurement to be as much as 625 lbs. per sq. inch above the pressure in the oil bath. 
These results obtained with the oil bath are very important, notwithstanding that 
the condition is not common in practice. They show that with perfect lubrication a 
definite law of variation of the friction with the pressure and velocity holds for a 
particular journal and brass. This strongly implies that the irregularity previously 
found was due to imperfect lubrication. Mr. Tower has brought this out:—Sub¬ 
stituting for the bath an oily pad, pressed against the free part of the journal, and 
making it so slightly greasy that it was barely perceptible to the touch, he again 
