U & V.

Undulation, swinging or vibrating.
Vacuum, a place void of air,
Valve, a sort of trap door.
Valves, what meant hy, II. 180.
Vegetables, how blanched, III. 79.
Velocity, a term applied to motion. Accelerating what

meant by, I. 56.
Venus, the planet, its distance from the sun; the velo-

city of its motion ; its magnitude, I. 312—315.
Why an evening and why a morning star, I. 315.

Transit of, what meant by, I. 316.
Vernier, its construction and use, II, 356.
Vertex, the top of any thing.
Vibration, the swinging motion of a pendulum.
Vision, the manner of, ÜI. 120.
Vdatile, any light substance that easily evaporates,
Voltaic batteries, III. 356–358. Shock, III. 357

359.
Voltaism, III. 356,f&c.
Wall, leaning one, at Bridgnorth, 1. 68.
Water, pure rain, the standard to compare other bo.

dies with, II. 97. Weighs the same every where.
ib. Always deeper than it appear to be, II. 153
and IH. 36. How raised from deep wells, II. 191
- 193. Formed of two gasses, III. 351. Decom-
posed, III. 367.

W.

Water-spouts, their cause, III. 318. How dispersed,

III. 319.
Weather, rales for judging of, II. 399--401.

Wedge, a triangular piece of wood or metal, to cleave

stone, &c. Its principle explained, I. 145. Its ad-
vantages 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 in-
creased, I. 128. Explained on the principle of the

lever, I. 131.
White, Mr. James, his invention of a crane, I. 130.

His patent pulley, I. 137.
Wind, what it is, II. 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, 11. 324.
Winds, how many kinds, and why so named, II.

315.
Winter, why colder than the summer, I. 247.

Y.

Year, its length, how measured, I. 265. Gregorian,

what meant by, I. 268. The beginning of, changed
from the 25th of March to the 1st of January,
I. 269.

2.

CONTENTS.

OF

VOL. III.

OPTICS.

18

Conversation

Page

I. Light: the Smallness and Velocity of its

Particles

9

II. Rays of Light:-Reflection and Refrac-

tion

III. Refraction of Light

27

IV. Refraction and Reflection of Light 35

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

67

IX. Colours

76

X. Reflected Ligbt and Plain Mirrors. 83

XI. Concave Mirrors

89

XIL Concave Mirrors Experiments

96
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

128

XVIII. Rainbow

134

XIX. Refracting Telescopes

143

XX. Reflecting Telescopes

153

XXI. Microscope

159

XXII. Camera Obscura, Magic Lanthorn, and

Multiplying Glass

173

MAGNETISM.

XXII. The Magnet

XXIV. Magnetic Attraction and Repulsion

XXV. Methods of making Magnets

XXVI. Mariners compass

183

189

195

202

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

XXXIII. The Leyden Phial

259

XXXIV. Lane's Electrometer, and the Elec-

trical Battery

268
Conversation

Page

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

XLI. Animal Electricity

330

XLII. Summary of Electricity

336