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number and complexity in proportion to the wealth and civilization of a state. Indeed these sorts of articles are, with respect to wealth, the cause and the effect. The student in mechanics being conversant with the elements of Conic Sections, will apply his knowledge to the investigation of the motions and paths of Projectiles, and of Central Forces. He will also be led to consider the properties and best mode of constructing different kinds of pendulums.

We shall reserve ourselves to the close of the department, Natural Philosophy, before we speak of those authors who have treated of the several subjects collectively, and only refer to a few who have given separate treatises on each distinct branch.

"An Introduction to Natural Philosophy" by John Keill, D. D. was published in Latin, and has gone through many editions in both languages. It contains the substance of Philosophical lectures read at the University of Oxford in the year 1700; and is well worthy of perusal, by those who can afford the time, without entirely neglecting some treatises of more modern date. The author's mode of demonstration is simple, but scientific, and in general it depends only upon the elements of geometry. Dr. Keill's first lecture shews the method of philosophizing: the next four treat of matter and its properties. The sixth lecture to the tenth inclusive, treats of motion, time, and place, in these, are descriptions and demonstrations of the properties of the mechanical powers. The laws of nature, and their application to the doctrine of percussion, are discussed in the four following lectures. The fifteenth and sixteenth lectures treat of the descent of heavy bodies on inclined planes; of the motion of pendulums; and of projectile forces. In several parts of these lectures the reader is supposed to be acquainted with Conic Sections, as well as common Geometry. And in a single instance his knowledge is required to extend to the doctrine of Fluxions. An appendix to the volume contains a demonstration of the Theorems of M. Huygens on the central forces. The title

to the Latin edition of this volume is "Introductio ad Veram Physicam." Hence it is often denominated Keill's Physics.

The book very much used at Cambridge, among the junior classes, is entitled "The Principles of Mechanics, designed for the use of students in the University," by James Wood, B. D. It is divided into sections treating of matter and motion-of the laws, composition, and resolution of motionof the mechanical powers, centre of gravity, and collision of bodies of accelerated and retarded motion-of the oscillations of bodies and of projectiles.

A more elaborate work, the performance likewise of a lecturer at Cambridge, is entitled. "A System of Mechanics, being the substance of lectures upon that branch of Natural Philosophy, by the Rev. T. Parkinson, M. A. This System of Mechanics is introduced by a very good account of the doctrine of Ratios.

"The Principles of the Mechanical Powers" are briefly and ably stated, in a small tract by Dr. Hugh Hamilton, already referred to as author of a valuable treatise on Conic Sections. The tract now alluded to, is one of a small volume entitled "Philosophical Essays." It has passed through several editions, the third was printed in 1772.

"Select Mechanical Exercises: shewing how to construct different clocks, orreries, and sun-dials, on plain and easy principles. With several miscellaneous articles; and new tables: (1) for computing the time of any new or full moon. (2) For graduating and examining the usual lines on the sector, plain scale, and gunter. Illustrated with copper

plates. To which is prefixed a short account of the life of the author. By James Ferguson, F. R.S." The title page of this work is sufficiently descriptive of its plan and object. The subjects discussed, will be found particularly interesting to those young persons who have a taste for practical mechanics. The biography of the author is simple, but calculated to awaken the best feelings in those for whose perusal it is evidently designed.

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CHAP. II.

NATURAL PHILOSOPHY,

Continued,

HYDROSTATICS, history of Fluid, definition of-Different branches of the science-Liquids, peculiarities of-Specific gravity-Gravity and pres. sure of fluids-Hydrostatical paradox-lateral pressure-Rules for obtaining the specific gravities of bodies-Writers on Hydrostatics: Cotes -Vince―Parkinson. PNEUMATICS-of the atmosphere and its properties-Experiments of Galileo and Torricelli-The air-pump-Experiments. HYDRAULICS: Pumps-Fire-engines-Air-gun—Artificial fountains-Condensing-machine. AcoUSTICS-Nature of sound illustrated— Echo-Writers on Pneumatics, &c. Clare-Smeaton. STATICS-DYNAMICS-Writers: Gregory-Atwood-Wilkins.

WE trace the history of the science of Hydrostatics, and those which depend upon it, chiefly to Archimedes, whose discoveries were such as to do the highest honour to his genius and penetration. He was the inventor of the mode of measuring the bulk of solids, by immersing them in fluids. This discovery was thought by his contemporaries, and by many who succeeded him in the path of philosophy, to indicate a degree of ingenuity almost incredible. Archimedes himself valued it very highly, and was enabled to apply it to the determination of the specific gravity of Hiero's crown, and to the

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