BY
WILLIAM DUANE ENNIS
_Professor of Mechanical Engineering in the Polytechnic
Institute of Brooklyn_
_123 ILLUSTRATIONS_
[Illustration: VAN NOSTRAND LOGO]
NEW YORK
D. VAN NOSTRAND COMPANY
23 MURRAY AND 1911 27 WARREN STS.
_Copyright, 1911, by_
D. VAN NOSTRAND COMPANY