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Trumpet, speaking, described, ii. 196-199. When
first used, ii. 198.

Trumpets, for deaf persons, ii. 199.

Tube, a pipe.

Twilight, the degree of light experienced between
sun setting, or rising, and dark night.

U & V

Undulation, swinging or vibrating.

Vacuum, a place void of air.
Valve, a sort of trap door.
Valves, what meant by, ii. 124.
Vegetables, how blanched, iii. 56.
Velocity, a term applied to motion.
what meant by, i. 41.

Accelerating,

Venus, the planet, its distance from the sun; the
velocity of its motion; its magnitude, i. 223,
225. Why an evening and why a morning star,
i. 225. Transit of, what meant by, i. 226,
Vernier, its construction and use, ii. 241.
Vertex, the top of any thing.

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, pure rain, the standard to compare other
bodies with, ii. 69. Weighs the same every
where, ib. Always deeper than it appears to be,
ii. 107, and iii. 36. How raised from deep wells,
ii 131, 132. Formed of two gases, iii. 244.
Decomposed, iii. 255.

Water-spouts, their cause, iii. 220. How dispersed,
ib.

Weather, rules for judging of, ii. 270—272.

Wedge, a triangular piece of wood or metal, to
cleave stone, &c. Its principle explained, i. 104.
Its advantages in cleaving wood, i. 105.
instruments referred to, i. 106.

What

Well, how to find the depth of one, i. 43.
Wheel and axis, described, i. 91. For what pur-
poses used, ib. Its power estimated, i. 92. How
increased, i. 92. Explained on the principle of
the lever, i. 95.

White, Mr. James, his invention of a crane, i. 95.
His patent pulley, i. 99.

Wind, what it is, ii. 212. The cause of, ii. 213. Ex-
periment on, ii. 213 and 217. Definition of, ii.
215. Its direction denominated, ib. The cause
of its variableness in England, ii. 217. How to
find its velocity, ii. 219. Table of, ii. 220.
Winds, how many kinds, and why so named, ii. 214,
Winter, why colder than the summer, i. 177.

Y

Year, its length, how measured, i. 190. Gregorian,
what meant by, i. 192. The beginning of, changed
from the 25th of March to the 1st of January, i.

193.


Zenith, that point of the heavens over one's head.
Zinc, experiment with, iii. 243.

Zodiac, a belt in the heavens, sixteen degrees broad,
through which the ecliptic runs. Signs of, i. 135.
Dr. Watts's lines on, i. 136.

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CONTENTS OF VOL. III.

OPTICS.

Conversation

Page

IX. Colours

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Rainbow

I. Light: the Smallness and Velocity of its
Particles

II. Rays of Light :-Reflection and Refraction
III. Refraction of Light

IV. Refraction and Reflection of Light
V. Different kinds of Lenses

VI. Parallel, diverging, and converging Rays
VII. Images of Objects-Scioptric Ball, &c.

VIII. Nature and Advantages of Light

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X. Reflected Light and Plain Mirrors

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XII. Concave Mirrors-Experiments

XIII. Concave and Convex Mirrors

XIV. Optical Deceptions, Anamorphoses, &c.
XV. Different parts of the Eye

XVI. Manner of Vision

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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

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Camera Obscura, Magic Lantern, and Mul-
tiplying Glass

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