Chapter XIV: Introduction: General Properties of Bodies. Impenetrability. Extension (12)

PNEUMATICS. That branch of natural philosophy, which treats of the mechanical properties of the atmosphere, or of air in general.

POLES. The extremities of the axis of motion either of our earth, or of any other revolving sphere. The poles of the earth have never been visited; the regions by which they are surrounded, being obstructed by impassable barriers of ice.

POWER. That force which we apply to any mechanical instrument, to effect a given purpose, is denominated power, from whatever source it may be derived. We have the power of weights, of springs, of horses, of men, of steam, &c.

PRISM. The instrument usually so called, is employed in optics to decompose the solar ray: it consists of a piece of solid glass, several inches in length, and having three flat sides; the ends are equal in size, and are of course triangular.

PRECESSION OF THE EQUINOXES. Every equinox takes place a few seconds of a degree, before the earth arrives at that part of the ecliptic in which the preceding equinox occurred. This phenomenon is called the precession of the equinoxes. There is consequently a gradual change of the places of the signs of the zodiac: a fact, the discovery of which has thrown much light on ancient chronology.

PROJECTION. That force by which motion is given to a body, by some power acting upon it, independently of gravity.

PULLEY. One of the six mechanical powers. A wheel turning upon an axis, with a line passing over it. It is the moveable pulley only, which gives any mechanical advantage.

PUMP. An hydraulic, or pneumatic instrument, for the purpose of raising water, or exhausting air.

QUADRANT. A quarter of a circle. An instrument used to measure the elevation of a body in degrees above the horizon.

QUADRATURES OF THE MOON. That period in which she appears in the form of a semicircle. She is then either in her first, or her last quarter; and exactly half way, between the places of new, and of full moon.

RADIATION. The passage of light or heat in rays, or straight lines; these being projected from every luminous, or heated point, in all directions.

RADIUS. The distance from the centre of a circle, to its circumference; or one half of its diameter. In the plural denominated radii.

RAINBOW. An appearance in the atmosphere, occasioned by the decomposition of solar light, in its refraction, and reflection, in passing through drops of rain. The bow can be seen, only when the sun is near the horizon, when the back is turned towards it, and there is a shower in the opposite direction.

RAY. A single line of light, emitted in one direction, from any luminous point.

REACTION. Every body, whether in a state of motion, or at rest, tends to remain in such state, and resists the action of any other body upon it, with a force equal to that action. This resistance, is called its _reaction_.

RECEIVER. This name is applied to glass vessels of various kinds, appertaining to the air pump, and from which the air may be exhausted. They are made to contain, or receive, any article upon which an effect is to be produced, by taking off the pressure of the atmosphere.

REFRACTION, of the rays of light, is the bending of those rays, when they pass obliquely from one medium into another of different density. A stick held obliquely in water, appears bent or broken at the surface of the fluid.

REFRANGIBILITY. Capacity of being refracted. Light is decomposed by the prism, because its component parts are refrangible in different degrees, by the same refracting medium.

REPULSION. The reverse of attraction. A tendency in particles, or in masses of matter, to recede from each other. The matter of heat within a body, appears to counteract the attraction of its particles, so as to prevent absolute contact.

RETINA. That part of the ball of the eye, upon which the images of visible objects are formed; and from which, the idea of such forms, is conveyed to the mind.

REVOLUTION, of a planet; is either diurnal, or annual; the former, is its turning upon its own axis; the latter, is its passage in its orbit.

SATELLITES. Moons, secondary planets.

SEGMENT OF A CIRCLE. A portion, or part of a circle; called also, an arc of a circle.

SEMI-DIAMETER. Half the diameter. The semi-diameter of the earth, is the distance from its surface, to its centre.

SIDERIAL. Belonging to the stars. A siderial day, is the time required for a star to reappear on a given meridian. A siderial year, the period in which the sun appears to have travelled round the ecliptic, so as to have arrived opposite to any particular star, from which his course was calculated.

SIGNS, or CONSTELLATIONS. Collections, or groups, of stars. Those of the zodiac are twelve, corresponding with the twelve months in the year. In the centre of these the ecliptic is situated. The sun appears to pass in succession through these signs; entering the first degree of Aries, which is accounted the first sign, about the 21st of March.

SKY. That vast expanse, or space, in which the heavenly bodies are situated. Its blue appearance is supposed to arise from the particles of which the atmosphere is composed, possessing the property of reflecting the blue rays, in greatest abundance.

SOLAR. Appertaining to, or governed by, the sun: as the solar system, the solar year, solar eclipses.

SOLID. Not fluid. Having its parts connected so as to form a mass. Solid bodies, are not absolutely so, all undoubtedly containing pores, or spaces void of matter.

SOLSTICES. The middle of summer and the middle of winter; those two points in the orbit of the earth, in which its poles point most directly towards the sun.

SONOROUS BODIES. Those bodies which are capable of being put into a state of vibration, so as to emit sounds.

SPECIFIC GRAVITY. The relative weight of bodies of different species, when the same bulk of each is taken. Water has been chosen as the standard for comparison. If we say that the specific gravity of a body is 6, we mean, that its weight is six times as great as that of a portion of water, exactly equal to it in bulk.

SPECTRUM. That appearance of differently coloured rays, which is produced by the refraction of the solar ray, by means of a prism, is called the prismatic spectrum; it exhibits most distinctly, and beautifully, all the colours seen in the rainbow.

SPHERE. A globe, or ball.

SPHEROID. Spherical; a body approaching nearly to a sphere in its figure. The earth, is denominated an _oblate spheroid_; it not being an exact sphere, but flattened at the poles, so as to cause the polar diameter to be upwards of thirty miles less than the equatorial. Oblate, is the reverse of oblong, and means shorter in one direction, than in another.

SPRING TIDES. Those tides which occur at the time of new, or of full moon. The tides then rise to a greater height than at any other period.

SQUARE. A figure having four sides of equal length, and its angles all right angles.

In numbers; the product of a number multiplied into itself; thus, the square of 3 is 9, and the square of 8 is 64.

STAR. The _fixed_ stars are so called, because they retain their relative situations; while the planets, by revolving in their orbits, appear to wander amongst the fixed stars.

SUBTEND. This term is applied to the measurement of an angle; when the lines by which it is bounded recede but little from each other, they are said to subtend; that is, to be contained under, a small angle.

SUPERFICIES. The surface of any figure. Space extended in length and width.

SYSTEM. The mutual connexion, and dependance of things, upon each other. The solar, or Copernican system, includes the sun, the planets, with their moons, and the comets.

TANGENT. A straight line touching the circumference of a circle; but which would not cut off any portion of it, were it extended beyond the touching point, in both directions.

TELESCOPE. An instrument by which distant objects may be distinctly seen; the images of objects being brought near to the eye, and greatly magnified.

TEMPERATE ZONES. Those portions of the surface of the earth situated between 23-1/2 and 66-1/2 degrees of latitude. Within these boundaries, the sun is never vertical; nor does he ever remain, during a whole day, below the horizon.

THERMOMETER. An instrument for measuring the temperature of the atmosphere, or of other bodies.

TORRID ZONE. That portion of the earth which extends 23-1/2 degrees on each side of the equator, to the tropical circles; within this limit, the sun is vertical, twice in the year.

TRANSIT. Mercury or Venus, are said to transit the sun, when they pass between the earth and that luminary. They then appear like dark spots, upon the face of the sun.

TRANSPARENT. Allowing the rays of light to pass freely through. The reverse of opaque. Glass, water, air, &c. are transparent bodies.

TROPICS. Two circles on the globe on either hemisphere, at the distance of 23-1/2 degrees from the equator. Beyond these circles, the sun is never vertical: and the countries within them, are denominated tropical.

TWILIGHT. That portion of the morning or evening, in which the light of the sun is perceptible, although he is below the horizon.

VACUUM. Space void of matter. Such is supposed to be the space in which the planets revolve. We are said to produce a vacuum, when we exhaust the air from a receiver.

VALVE. A part of a pump, and of some other instruments, which opens to admit the passage of a fluid in one direction, but closes when pressed in the opposite direction, so as to prevent the return of the fluid; a pair of bellows is furnished with a valve.

VAPOUR. Exhalations from fluid or solid substances, generally mixing with the atmosphere. The most abundant, is that from water.

VERTICAL. Exactly over our heads: ninety degrees above our horizon.

VIBRATION. The alternate motion of a body, forwards and backwards; swinging, as a pendulum.

VISUAL. Belonging to vision; as the visual angle, or that angle formed by the rays of light which enter the eye, from the extremities of any object.

UNDULATION. A vibratory, or wave-like motion communicated to fluids. Sound, is said to be propagated by the undulatory, or vibratory motion of the air.

WEDGE. One of the mechanical powers; the form of the wedge is well known. It is of extensive use; serving to rend bodies of great strength, and to raise enormous weights.

WHEEL AND AXLE. One of the mechanical powers, used under various modifications. Cranes for raising weights, the wheels and pinions of clocks and watches, windlasses, &c. are all applications of this power.

ZODIAC. A broad belt in the heavens, extending nearly eight degrees on each side of the ecliptic; the planes of the orbits of all the planets are included within this space. This belt is divided into twelve parts or signs, each containing 30 degrees.

These signs are:

_Aries_; the Ram.
_Taurus_; the Bull.
_Gemini_; the Twins.
_Cancer_; the Crab.
_Leo_; the Lion.
_Virgo_; the Virgin.
_Libra_; the Scales.
_Scorpio_; the Scorpion.
_Sagittarius_; the Archer.
_Capricornus_; the Goat.
_Aquarius_; the Waterer.
_Pisces_; the Fishes.

The first six are called northern signs; because the sun is in them, during that half of the year, in which he is vertical to the north of the equator; the last six, are called southern signs; because, during his journey among them, he is vertical to the south of the equator.

The sun enters _Aries_, at the time of the _vernal equinox_; _Cancer_, at the _summer solstice_; _Libra_, at the _autumnal equinox_; and _Capricornus_, at the _winter solstice_.

The sun is said to enter a sign, when the earth in going round in its orbit, enters the opposite sign. Thus, when the sun appears in the first degree of _Libra_, it is in consequence of the earth having arrived opposite to the first degree of Aries. A line then drawn from the earth, and passing through the centre of the sun, would, if extended to the fixed stars, touch the first degree of Libra.

ZONE. The earth is divided into zones, or belts. See FRIGID, TEMPERATE, and TORRID ZONES.

INDEX.

A.

Air, 11, 15, 28, 50, 136.

Air-pump, 31, 145.

Angle, 44.
acute, 44.
obtuse, 44.
right, 44.
of incidence, 45, 154, 160, 173.
of reflection, 45, 154, 160, 173.
visual, 168, 169, 170.

Angular velocity, 171.

Antarctic circle, 92.

Aphelion, 75.

Arctic circle, 92.

Atmosphere, 28, 104, 129, 136, 144, 150, 163.
colour of, 193.
reflection of, 193.
refraction of, 182.

Attraction, 10, 14, 23, 25, 179.
of cohesion, 15, 19, 118.
capillary, 18.
of gravitation, 18, 23, 29, 70, 80, 96, 116, 136.

Avenue, 170.

Auditory nerve, 151.

Axis, 78.
of motion, 48.
of the earth, 22, 99.
of mirrors, 176.
of a lens, 184.

B.

Balloon, 30.

Barometer, 140.

Bass, 155.

Bladder, 138.

Bodies, 10.
elastic, 40.
fall of, 23, 26, 30, 36.
luminous, 157.
opaque, 157.
sonorous, 152, 155.
transparent, 157.

Bulk, 16.

C.

Camera obscura, 184, 197, 201.

Capillary tubes, 18.

Centre, 48.
of gravity, 48, 51, 52, 115.
of magnitude, 48, 53.
of motion, 48, 55, 115.

Centrifugal force, 49, 72, 95, 115.

Centripetal force, 49, 72.

Ceres, 84.

Circle, 44, 94.

Circumference, 94.

Clouds, 129.

Colours, 23, 185.

Comets, 86.

Compression, 42.

Concord, 155.

Constellation, 86.

Convergent rays, 175, 177.

Crystals, 12.

Curvilinear motion, 47, 72.

Cylinder, 52.

D.

Day, 78, 105, 106.

Degrees, 44, 94, 99, 169, 170.
of latitude, 94, 112.
of longitude, 94, 112.

Density, 16.

Diagonal, 47.

Diameter, 94.

Discords, 155.

Diurnal, 78.

Divergent rays, 175, 177.

Divisibility, 10, 12.

E.

Earth, 18, 70, 84, 88, 95.

Echo, 154.

Eclipse, 110, 159.

Ecliptic, 86, 92, 99.

Elasticity, 41.

Elastic bodies, 28, 40.
fluids, 28, 41, 118, 136.

Ellipsis, 75.

Equinox, 100, 107.
precession of, 107.

Equator, 92, 99.

Essential properties, 10.

Exhalations, 13.

Extension, 10, 11.

Eye, 166, 195.

F.

Fall of bodies, 24, 27, 31.

Figure, 10, 12.

Fluids, 118, 128.
elastic, 28, 41, 118, 136.
equilibrium of, 120, 122, 132.
non-elastic, 119.
pressure of, 121.

Flying, 40.

Focus, 176.
of concave mirrors, 177.
of convex mirrors, 175, 177.
of a lens, 184.
imaginary, 176.
virtual, 176.

Force, 33.
centrifugal, 49, 72, 95, 115.
centripetal, 49, 72.
projectile, 47, 49.
of gravity, 47, 49.

Fountains, 135.

Friction, 68, 69, 135.

Frigid zone, 93.

Fulcrum, 54.

G.

General properties of bodies, 10.

Georgium Sidus, 85.

Glass, 183.
burning, 188.
refraction of, 183.

Gold, 119, 126.

Gravity, 18, 23, 78, 97.

H.

Harmony, 155.

Heat, 16, 29, 103.

Hemisphere, 92, 100.

Herschel, 85.

Hydraulics, 118.

Hydrometer, 128.

Hydrostatics, 118.

I.

Image on the retina, 165, 172.
reversed, 167.
in plain mirror, 172.
in concave do. 175.
in convex do. 175.

Impenetrability, 10.

Inclined plane, 54, 66.

Inertia, 10, 14, 32.

Inherent properties, 10.

Juno, 84.

Jupiter, 85.

L.

Lake, 133, 135.

Latitude, 94, 112.

Lens, 184.
concave, 184.
convex, 184.
meniscus, 184.
plano-concave, 184.
plano-convex, 184.

Lever, 54, 55.
first kind, 58.
second kind, 60.
third kind, 60.

Light, 157.
pencil of, 158.
of the moon, 162, 163.
absorption of, 188.
reflected, 160.
refraction of, 179.

Liquids, 118.

Longitude, 94, 112.

Luminous bodies, 157.

Lunar month, 108.
eclipse, 110.

M.

Machine, 54, 66.

Magic lanthorn, 203.

Mars, 84.

Matter, 10, 13.

Mechanics, 32.

Mediums, 157, 180.

Melody, 156.

Mercury, (planet) 83, 85, 114.

Mercury, or quicksilver, 16, 140, 141.

Meridians, 93.

Microscope, 200.
single, 200.
double, 200.
solar, 202, 203.

Minerals, 12.

Minutes, 94.

Momentum, 38, 56.

Monsoons, 149.

Month, lunar, 108.

Moon, 78, 79, 80, 82, 85.

Moonlight, 162, 163.

Motion, 14, 32, 36.
accelerated, 36.
axis of, 48.
centre of, 48, 55.
compound, 46.
curvilinear, 47, 49.
diurnal, 78.
perpetual, 35.
retarded, 35.
reflected, 43.
uniform, 34.

Mirrors, 172.
axis of, 176.
burning, 177.
concave, 174, 176, 209.
convex, 174, 175.
plane or flat, 172.
reflection of, 173.

N.

Neap tides, 116.

Nerves, 166.
auditory, 151, 166.
olfactory, 166.
optic, 164, 166.

Night, 78.

Nodes, 110.

O.

Octave, 156.

Odour, 13.

Opaque bodies, 157, 158.

Optics, 157.

Orbit, 86.

P.

Pallas, 84.

Parabola, 51.

Parallel lines, 25.

Parallel of latitude, 94.

Pellucid bodies, 157.

Pencil of rays, 158.

Pendulum, 98.

Perihelion, 75.

Perpendicular lines, 25.

Phases, 109.

Piston, 143, 145.

Plane, 92, 93.

Planets, 76, 81, 83.

Poles, 92, 99, 100.

Polar star, 100, 112.

Porosity, 42, 126.

Powers, mechanical, 54.

Projection, 49, 50, 71.

Precession of equinoxes, 107.

Pulley, 54, 63.

Pump, 31.
sucking and lifting, 143.
forcing, 144, 145.
air, 31, 145.

Pupil of the eye, 164.

R.

Rain, 17, 129.

Rainbow, 188.

Rarity, 16.

Ray of light, 158, 179.
reflected, 160, 161.
incident, 161.

Rays, intersecting, 165.

Reaction, 39.

Receiver, 31.

Reflection of light, 160, 163.
angle of, 45, 161, 173.
of mirrors, 173.
of plane mirrors, 174.
of concave do. 174.
of convex do. 174.

Reflected motion, 43.

Refraction, 179, 186.
of the atmosphere, 182.
of glass, 183.
of a lens, 184.
of a prism, 185.

Resistance, 54.

Retina, 165.
image on, 166.

Rivers, 134.

Rivulets, 131.

S.

Satellites, 80, 111, 113.

Saturn, 85.

Scales, or balance, 55.

Screw, 54, 67.

Shadow, 110, 111.

Siderial time, 106.

Sight, 165.

Signs of the zodiac, 86, 93.

Smoke, 14, 29.

Solar microscope, 202.

Solstice, 100, 102.

Sound, 151.
acute, 155.
musical, 155.

Space, 33.

Specific gravity, 123.
of air, 140.

Spectrum, 190.

Speaking-trumpet, 154.

Sphere, 26.

Springs, 130.

Spring tides, 116.

Square, 81, 85.

Stars, 77, 86, 102.

Storms, 147.

Substance, 10.

Summer, 76, 100.

Sun, 71, 75, 78, 162, 182.

Swimming, 41.

Syphon, 132.

T.

Tangent, 49, 73.

Telescope, 203, 204.
reflecting, 204.
refracting, 204.

Temperate zone, 92, 101.

Thermometer, 142.

Tides, 114, 116.
neap, 116.
spring, 116.
aerial, 150.

Time, 105, 107.
siderial, 107.
equal, 107.
solar, 107.

Tone, 155.

Torrid zone, 93, 147, 182.

Transit, 114.

Transparent bodies, 157.

Treble and bass, 155.

Tropics, 92.

V.

Valve, 143.

Vapour, 17, 29, 104, 129.

Velocity, 33, 57.

Venus, 84.

Vesta, 84.

Vibration, 98, 152.

Vision, 164, 168.

Vision, angle of, 168, 170.
double, 171.

U.

Undulation, 153.

Unison, 155.

W.

Water, 118, 130.
spring, 130.
rain, 130.
level of, 120.

Wedge, 54, 66.

Weight, 23.

Wheel and axle, 54, 65.

Wind, 146.
trade, 147.
periodical, 148.

Winter, 76, 101.

Y.

Year, 107.
siderial, 107.
solar, 107.

Z.

Zodiac, 86.

Zone, 93.
torrid, 93, 147, 182.
temperate, 93, 101.
frigid, 93, 100.

THE END.

TO ALL TEACHERS.

SCHOOL BOOKS.

SMILEY'S GEOGRAPHY AND ATLAS, and SACRED AND ANCIENT GEOGRAPHY FOR SCHOOLS.

The above works will be found useful and very valuable as works
of reference, as well as for schools. The Maps, composing the
Atlases, will be found equal in execution and correctness to
those on the most extensive scale. The author has received
numerous recommendations, among which are the following:

Dear Sir--I have looked over your "_Easy Introduction to the
Study of Geography_," together with your "_Improved Atlas_." I
have no hesitation in declaring, that I consider them works of
peculiar merit. They do honour to your industry, research, and
talent, and I am satisfied, will facilitate the improvement of
the student in geographical science.

With sentiments of sincere consideration, I am yours truly,

WM. STAUGHTON, D. D.
_President of Columbia College, District of Columbia._

MR. THOMAS SMILEY.
_Philadelphia, Sept. 1, 1823._

* * * * *

_Extract from the Minutes of the Philadelphia Academy of
Teachers._

_November 1, 1823._

Resolved unanimously, That the Academy of Teachers highly
approve the superior merits of Mr. Smiley's "_Easy Introduction
to the Study of Geography_," and the accompanying Atlas, and
cordially recommend them to the patronage of the public.

B. MAYO, _President._