Few subjects related to the design or construction of machinery are of greater importance than the subject of bearings. All classes of mechanisms have bearings of some kind and bearings that are properly designed and constructed are a necessity. As every experienced mechanic knows, a poor bearing may tie up a machine or even cause an entire plant to shut down temporarily. Owing to the importance of this subject, designers and mechanics in general should understand the fundamental principles governing bearing design and should know what approved types are in common use on different classes of machinery. This treatise deals exclusively with plain bearings, ball and roller bearings being covered in another book of this series. The types of plain bearings illustrated in a connection with the following chapters were selected to show how designs are modified to suit different conditions, and also practical methods of arranging bearings to insure adequate lubrication and thorough protection against the entrance of any foreign material liable to injure the bearing surfaces. The designs illustrated were taken from actual practice and have proved satisfactory when properly constructed and applied. This treatise contains, in addition to the features mentioned, condensed information on corn- positions of various bearing metals, their properties, the classes of service to which different bearing alloys are adapted, and the general methods of procedure in designing plain bearings to meet different service conditions.