<div class="htmlview paragraph">The authors state that the coefficient of friction between two rubbing surfaces is influenced by a very large number of variables, the most important being, in the case of an oiled journal, the nature and the shape of the surfaces, their smoothness, the clearance between the journal and the bearing, the viscosity of the oil, the “film-forming” tendency or “oiliness” of the oil, the speed of rubbing, the pressure on the bearing, the method of supplying the lubricant and the temperature. The primary object of the paper is to present the best available data regarding the fundamental mechanism of lubrication so as to afford a basis for predicting the precise effect of these different variables under any specified conditions.</div> <div class="htmlview paragraph">Definitions of the terms used are given and the laws of fluid-film lubrication are discussed, theoretical curves for “ideal” bearings being treated at length. The application of the recommended method of plotting to data in the literature of the subject is described, the thought then including consecutively oiling method and oiliness-factor effects; the effect of variable clearance; bearing metal and clearance effects on the critical point of film rupture; oiliness and miscellaneous effects. A summary is given of the essential conclusions and a description of the method of their application to practical problems.</div>