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PREFACE. IX On reviewing the whole history of the engine to date, it will be seen that progress continues in the directions already pointed out and towards still higher steam-pressures, higher speeds of piston and of rotation, increased ratios of expansion in multiple-cylinder engines, and with constant reduction of the now^ well-understood waste which distinguish the real from the ideal steam-engine. The Publishers have, in this edition, effected a great improvement in the matter of book-making, by enlarging its page ; securing thus broader margins and a vastly more satisfactory volume both to the eye and to the hand. They unite with the Author in cordially acknowledging a real indebtedness to those engineers, engine-builders, and "business firms who have so liberally and promptly aided them in the endeavor to make the sixth edition of this work thoroughly modern, by supplying all information sought from them, and in so many ways facilitating the work of effective revision and extension. It is also a pleasure, as well as a duty, on the part of both Author and Publishers, to make hearty acknowledgment of their debt to that class of readers, extensive and evidently appreciative, if not always claiming to rank as mathematicians or men of science, who find sufficient instruction and enough of interest in a semi-popular work of this character to call for six editions in so short a period. It is hoped that equal satisfaction may be given in subsequent editions — if they should be called for during the remaining years of the life of the steam-engine in the character of man's greatest and grandest aid in energy-transformation for useful purposes.

February, 1899.