Much Of the material in this work has been arranged after ex tended visits to drafting rooms in which the work in valve gears was being carried on in a practical way, and it is believed that the methods here presented will be found to agree fairly well with general practice. In writing up the descriptions Of the practical forms of valves and valve gears the author has received numerous courtesies from manufacturers which are hereby acknowledged. It has been the rule to have the manufacturer Of the valve or gear or engine described to pass finally on the accuracy Of the description and Of the illustrations that appear in this work. Every illustration has been newly prepared for this edition. In order to avoid the use of subscripts in numbering the illustrations and paragraphs as the work Of preparation proceeded, and as changes and additions were made, the author laid out the work originally by leaving ten numbers free at the end Of each section. It will be found that these numbers have been all used at the end Of some of the sections and that none have been used at the end Of other sections. The page numbers, however, are in consecutive order throughout the book.