FOREWORD.

I believed it necessary to suspend the printing of this Volume in order to insert them Referring to the new observations and corrections mentioned on the previous page regarding the Notre-Dame bridge machine., and at the same time to correct several essential passages based on certain commonly accepted principles of Hydraulics The branch of science and technology concerned with the mechanical properties of liquids., in which I perceived errors, as the reader will soon be convinced.

These matters appeared to me of such great consequence as to require no compromise; I set myself above the murmurs that might arise from the Subscribers original: "Souscripteurs." Individuals who paid in advance to fund the publication of the book, often growing impatient with delays. and my Bookseller original: "Libraire." In the 18th century, the bookseller often acted as the publisher and financier of the work., flattering myself that the fair-minded Public would approve of my conduct as soon as this Work appeared, enriched with the additions for which I felt the necessity; and to encourage this favor, I have accompanied this volume with all the magnificence of which it could be capable.

Having made only a slight mention in the Preface of the first volume regarding the subjects to be treated in this one, here are those contained in the third and fourth Books, according to the order deemed most appropriate for them.

The third Book is divided into five Chapters. The first begins with a Dissertation on the properties of air, deduced from a great number of experiments, accompanied by useful remarks, serving as an introduction to physics original: "physique." Here meaning natural philosophy or the mechanical sciences. and the theory of pumps.

The second includes the manner of calculating the force of the wind, and the greatest effect of the various machines that can be set in motion by its action.

In the third, one finds a reasoned description of pumps of all kinds, and an extensive theory on the manner of exactly calculating their effect.

The fourth includes the description of a large number of fine machines executed in France and in foreign countries, for raising water with pumps set in motion by the force of men, of hor-