Trumpet, speaking, described, ii. 196-199. When Trumpets, for deaf persons, ii. 199. Tube, a pipe. Twilight, the degree of light experienced between U & V Undulation, swinging or vibrating. Vacuum, a place void of air. Accelerating, Venus, the planet, its distance from the sun; the Vibration, the swinging motion of a pendulum. Vision, the manner of, iii. 84. Volatile, any light substance that easily evaporates. Voltaic batteries, iii. 247–248. 249. Voltaism, iii. 247, &c. Shock, iii. 247– W Wall, leaning one, at Bridgnorth, i. 50. Water-spouts, their cause, iii. 220. How dispersed, Weather, rules for judging of, ii. 270—272. Wedge, a triangular piece of wood or metal, to What Well, how to find the depth of one, i. 43. White, Mr. James, his invention of a crane, i. 95. Wind, what it is, ii. 212. The cause of, ii. 213. Ex- Y Year, its length, how measured, i. 190. Gregorian, 193. Ꮓ Zenith, that point of the heavens over one's head. Zodiac, a belt in the heavens, sixteen degrees broad, CONTENTS OF VOL. III. OPTICS. Conversation Page IX. Colours Rainbow I. Light: the Smallness and Velocity of its II. Rays of Light :-Reflection and Refraction IV. Refraction and Reflection of Light VI. Parallel, diverging, and converging Rays VIII. Nature and Advantages of Light X. Reflected Light and Plain Mirrors XII. Concave Mirrors-Experiments XIII. Concave and Convex Mirrors XIV. Optical Deceptions, Anamorphoses, &c. XVI. Manner of Vision XVII. Spectacles, and their Uses XVIII. XIX. Refracting Telescopes XX. Reflecting Telescopes XXI. XXII. Microscope 15 20 26 32 37 43 48 53 59 63 68 Camera Obscura, Magic Lantern, and Mul- |