In order to render this book useful to those who employ, or are employed about, Steam Engines, I have included in it various rules and practical data formerly published in my "Essay on the Boilers of Steam Engines," and have endeavoured to embody the necessary information relative to such improvements in principle or construction as have come into practical use since the date of the former publication. This will, therefore, probably supersede the necessity of a new edition of that work. Robert Armstrong 65, Fenchurch Street, London. 1862