The necessity for a revision and enlargement of this work is due to the approbation bestowed upon it by Machinists, and repeated requests from Engineers and Firemen that Air Brakes, Break Downs, Blows and Pounds, of a locomotive be treated with its construction. This I have endeavored to do, the best authorities on each subject being frequently consulted; how far my execution has corresponded with my design is for the reader to decide. Believing that the language of a mechanical book should be understood rather than admired, I have made no attempt at what is called fine writing, but have used as plain and familiar language as the exceedingly technical character of the subject would permit.