IV 
INTRODUCTION. 
been in use and the various forms in which it has been tried, is in many 
respects vague and speculative, as is proved by the different arrangements and 
proportions in which we find it continues to be constructed. 
All that can be done in the present state of our subject is to submit impartially 
the best facts which can be obtained, and, where inference is unavoidable, to guard 
the reader against taking probabilities for certainties. With this qualification, 
the author trusts that the following pages,—as they contain, in addition to the 
analysis which he has attempted, a quantity of information regarding the history 
of the invention and its various modifications that have not before been offered 
to the public, — will in some degree contribute to enlarge and classify our 
knowledge upon this novel method of giving motion to steam vessels.