Wedge, a triangular piece of wood or metal, to cleave stone, &c. Its principle explained, I. 145. Its advantages in cleaving wood, I. 146. What instru ments referred to, I. 147. Well, how to find the depth of one, I. 58. Wheel and axes described, I. 126. For what purposes used, ib. Its power estimated, I. 127. How increased, I. 128. Explained on the principle of the lever, I. 131. White, Mr. James, his invention of a crane, I. 130. His patent pulley, 1. 137. Wind, what it is, 11. 312. The cause of, II. 313. Experiment on, II. 314 and 319. Definition of, II. 315. Its direction denominated, ib. The cause of its variableness in England, II. 320. How to find its velocity, II. 322. Table of, II. 324... Winds, how many kinds, and why so named, I. 315. Winter, why colder than the summer, I. 247. Year, its length, how measured, 1. 265. Gregorian, what meant by, I. 268. The beginning of, changed from the 25th of March to the 1st of January, 1. 269. Zenith, that point of the heavens over one's head. through which the ecliptic runs. Signs of, I. 186. Dr. Watts's lines on, I. 189. CONTENTS. VOL. III. OPTICS. Page 1. Light: the Smallness and Velocity of its II. Rays of Light:-Reflection and Refrac- III. Refraction of Light - - - 27 IV. Refraction and Reflection of Light V. Different kind of Lenses - - 44 VI. Parallel, diverging, and converging Rays 52 VII. Images of Objects-Scioptric Ball, &c. 60 VIII. Nature and Advantages of Light - X. Reflected Light and Plain Mirrors. XI. Concave Mirrors ... . Conversation Page XIII, Concave and Convex Mirrors - 101 XIV. Optical Deceptions, Anamorphoses, &c. 107 XV. Different Parts of the Eye .. - 114 XVI. Manner of Vision - - - - 120 XVII. Spectacles, and their Uses MAGNETISM. ; XXIII. The Magnetic - - - 185 ELECTRICITY. XXVII. Early History of Electricity . 211 XXVIII. Electrical Attraction and Repulsion 217 XXIX. Electrical Machine - . 226 xxx. Electrical Machine - - - 234 XXXI. Electrical Attraction and Repulsion 242 XXXII. Electrical Attraction and Repulsion 254 VXXIII. The Leyden Phial - - - 259 XXXV. Experiments with the Battery - 276 XXXVI. Miscellaneous Experiments - 287 XXXVII. Electrophorus, Thunder-House, &c. 295 XXXVIII.Atmospherical Electricity • 301 XXXIX. Aurora Borealis ; Water-spouts”; Earthquakes . . . 210 XL. Medical Electricity - - - 324 GALVANISM, OR VOLTAISM. XLIII. The Origin of Galvanism - . XLIV. Galvanic Light and Shocks - XLV. Voltaic Conductors, Circles, Tables, - - |