INTRODUCTION.

In the practice of a Civil Engineer, much of his success depends on a sound knowledge of the principles of the motion of fluids, and of the circumstances attending such motions; at the same time, few have leisure to enter into such inquiries, unless they be brought before them in a condensed form, with clear directions for their immediate application to practice.

A work of this nature having been published in Germany by Professor Eytelwein, an abstract or summary of its contents was drawn up by Dr. Thomas Young, with such modifications and improvements as he considered would add to its value to an English reader. This summary was first published in the Journals of the Royal Institution in 1802, and the importance of so comprehensive a view of the doctrine of hydraulics, being immediately connected with the preceding experimental papers, was so evident, that we solicited Dr. Young's permission to republish it, and it was granted in the most kind and liberal manner; but, in consequence of his not having there

distinguished the extent to which we are indebted to Dubuat for forming the theorems given by Eytelwein, Dr. Young was desirous to add the following passage from his article, Hydraulics, in Napier's "Supplement to the Encyclopædia Britannica :"-" It has happened, "It from a combination of accidental circumstances, that Dubuat has been deprived of a considerable portion of his just merits, in favour of Mr. Eytelwein, without any kind of voluntary plagiarism on the part of that very respectable professor. The author of the English abstract of his work was acquainted with Dubuat's book, only from having read the extracts copied from it by Professor Robison, in his contributions to the Encyclopædia Britannica, and he was hence led into the mistake of supposing Professor Eytelwein the author of many improvements, which he had no more idea of claiming than he could have had of several modifications introduced into the Summary of Hydraulics,' chiefly extracted from his book, which appeared in the Journal of the Royal Institution, and which have been quoted as Eytelwein's."

To this Summary we have added a few notes, and given the rules in words at length in those instances where Dr. Young had not done so; and we have also added references to the experimental papers of Smeaton and Venturi. — EDITOR.

A

SUMMARY

OF THE MOST USEFUL PARTS

OF

HYDRAULICS.

THE theory of hydraulics has never been carried to a very high degree of perfection upon mathematical foundations alone; nor has it hitherto, even with the assistance of experiment, been rendered of much practical utility. Newton began the investigation of the motion of fluids. Daniel Bernoulli added to Newton's propositions much valuable matter, both from calculation and from experiment. D'Alembert and many later authors have exercised their analytical talents in inquiries of a similar nature. But another and a more practical mode of attaining hydraulic knowledge has been attempted by a distinct class of investigators, at the head of whom stands Chevalier Dubuat. These have begun from experiment alone, and have laboriously deduced, from very ample observations of the actual results of various particular cases, the general laws by which the phenomena appear to be regulated, or, at least, the formulas by which the effect of new combinations may be predicted. But it must be confessed that these formulas, however accurate, are too intricate to be retained in the memory, or to be very easily applied to calculations from particular data.

as

Mr. Eytelwein, a gentleman already known to the public by his translation of Dubuat's work into German, with important additions of his own, and honoured with several employments and titles relative to the public architecture of the Prussian dominions, has collected into this compendium of mechanics and hydraulics the principal facts that have been ascertained, as well by his own experiments as by those of former authors, especially such as are the most capable of practical application; and he appears to have done this in so judicious a manner, to make his book a most valuable abstract of every thing that can be deduced from theory respecting natural and artificial hydraulics. This elegant conciseness deserves so much the more praise, as his countrymen in general appear too often to make a merit of prolixity; and we shall have occasion to remark, that, besides the convenience of simplicity, he has sometimes been fortunate enough to unite with it the advantage of superior accuracy.

The first part of the work is but short; it relates to proper mechanics, and has little that is remarkably new or interesting. In treating of pendulums, the author informs us, with reference to another work of his own, that the Rhinland or Brandenburg foot contains 139.13 French lines. Hence it appears that 100 Rhinland feet are exactly 103 English; and in this paper the measures will be reduced accordingly.

The second part, relative to hydraulics, contains, besides a short Introduction, twenty-four chapters, almost every one of which presents to us something of importance.

CHAPTER I.

Of the Motion of Water flowing out of Reservoirs, and of the Contraction of the Stream.

The velocity of water, flowing out of a horizontal aperture, is as the square root of the height of the head of the water.

That is, the pressure, and, consequently, the height, is as the square of the velocity; for the quantity flowing out in any short time is as the velocity; and the force required to produce a velocity in a certain quantity of matter, in a given time, is also as that velocity; therefore, the force must be as the square of the velocity. The proposition is fully confirmed by Bossut's experiments the proportional velocities, with a pressure of 1, 4, and 9 feet, being 2722, 5436, and 8135, instead of 2722, 5444, and 8166; a very inconsiderable difference.

There is another mode of considering this proposition, not mentioned by Eytelwein, which is a very good approximation. Supposing a very small cylindrical plate of water immediately over the orifice to be put in motion at each instant, by means of the pressure of the whole cylinder standing on it, and supposing all the gravitation of the column to be employed in generating the velocity of the small cylindrical plate, neglecting its own motion; this plate would be urged by a force as much greater than its own weight as the column is higher than itself; and this, through a space shorter in the same proportion than the height of the column. But where the forces are inversely as the spaces described, the final velocities are equal. Therefore, the velocity of the water flowing out must be equal to that of a heavy body falling from the height of the head of water,