The object of this series of articles has been to form a basis of understanding of lubrication matters from which the reader may advance to further study, and which should be known to every lubrication engineer, works chemists who deal with lubricants, and all engineers who are responsible for the use of lubricating oils and greases in any quantity. We have not yet dealt with the practical side of lubrication at all. We shall do so in later articles and shall cover the simple methods of application.