OR, ELEMENTARY INSTRUCTION IN THE VARIOUS DEPARTMENTS OF LITERATURE AND SCIENCE; WITH Practical Rules FOR STUDYING EACH BRANCH OF USEFUL KNOWLEDGE. BY THE REV. W. SHEPHERD, AND THE REV. LANT CARPENTER, LL.D. Third Edition. IN TWO VOLUMES. VOL. II. LONDON: PRINTED FOR LONGMAN, HURST, REES, ORME, AND BROWN, PATERNOSTER-ROW. 1822. PRACTICAL ESSAY, &c. CHAP. I. ON NATURAL PHILOSOPHY. MECHANICS, definition of— connected with the Arts of Life - allied to Geometry. — History of Mechanics; what included under. Centrifugal and Centripetal forces. Mechanical Powers: LeverWheel and Axle - Pulley Inclined Plane-Wedge and the Screw. Writers on Mechanics: Robison — Keill — Wood - Parkinson Gregory — Ferguson. IN a course of natural philosophy, it is usual to place Mechanics at the head, because the knowledge of every other department depends in a great measure upon the right apprehension of the theory of this. Mechanics may be defined "the science which treats of the laws of the equilibrium and motion of solid bodies; of the forces by which they act upon one another; and of the means by which these actions may be increased or modified." As the practical part of this science is closely connected with the arts of life, and particularly with those which existed even in the rudest ages of society, the construction of machines must have been understood and practised in some way or other, long before any theory could have been invented, or even thought of. Hence, at a very early period, we read of the use of the lever, the pulley, the capstan, and other simple machines, long before the principles of |