A PISTON is a cylinder fitted to diminished, the different portions of the atmo

work air-tight in a tube.

NOTE 1.-If a tube of an indefinite length be placed in an upright position, the lower end being immersed in water; and if a piston fitting the tube be first placed in contact with the water, and then drawn upward, the water will follow the piston to the hight of thirty-four feet, at which hight it will cease to follow the piston, and will remain stationary, leaving a vacuum between its surface and the end of the piston. The cause of the ascent of the water in the tube is the pressure of the atmosphere on the surface of the water in which the lower end of the tube is

immersed; and the reason why the water will not follow the piston beyond the hight of thirtyfour feet is, that a column of water thirty-four feet high balances, by its weight, a column of air of the same diameter, extending to the upper limits of the atmosphere.

NOTE 2.-Mercury will follow a piston but thirty inches-a column of mercury thirty inches high being as heavy as a column of water thirtyfour feet high.

sphere would no longer be in equilibrium, and, consequently, the lighter portion would yield to the pressure of the heavier air surrounding it, and thus both the heavier and the lighter portions of the air would begin to move, or, in other words, wind would be produced.

NOTE 2.-Heat expands air, and thus renders it lighter. The winds, therefore, depend on the circumstance that different portions of the atmosphere are unequally heated by the sun's rays.

TO BLOW is to move as air.

A BLAST is a forcible blowing. (Ger. blasen, to blow.)

A PUFF is a sudden wind of moderate force and momentary duration. To Puff is 1. To drive air from the mouth in a single and quick blast. 2. To praise with exaggeration.

To Puff up is to swell with wind. A GUST is a sudden wind of conSUCTION is the formation of a vacu-siderable force, but of brief duration. um by a piston or other mechanical means, into which some liquid is forced by atmospheric pressure.

A VALVE is a small lid turning on a hinge, and permitting, when open, the passage of a fluid; and, when shut, preventing its return.

A SQUALL is a violent wind of short continuance.

A BREEZE is a moderate and steady wind.

A GALE is a strong wind.

A STORM is 1. And properly, a violent wind. 2. Wind accompanied by A PUMP is an apparatus for raising water by the agency of atmos-of rain, hail, or snow, though attended rain, hail, or snow. 3. A heavy fall pheric pressure, and consists of a with but little wind. tube, a piston, and two valves, the lower valve being stationary, and the other being inserted in the piston.

A TEMPEST is a violent storm of

wind, usually accompanied with rain, hail, or snow.

A BAROMETER is an instrument for measuring the weight of the atmos-lent storm of wind. A HURRICANE is an extremely vio

phere. It consists of a glass tube A WHIRLWIND is a wind characterabout thirty-three inches in length, ized by a rapid, whirling motion. which, being closed at one end and A TORNADO is a whirlwind of exopen at the other, is filled with mer-treme violence. (From the root of cury, and is then inverted in a cup turn.)

of mercury.

NOTE 1.-The mercury in the barometer, at

A WATERSPOUT is a whirlwind ac

the level of the sea, will stand at different hights, companied by a black, conical, or varying from twenty-eight to thirty-one inches, funnel-shaped cloud with the vertex according to the varying weight of the atmos-pointing downward.

phere.

NOTE 2.-The barometer may be used for determining the hight of mountains, since the mercury sinks in the tube, according to a fixed law, as we ascend above the level of the sea.

WIND is air in motion.

NOTE 1.-Waterspouts frequently suck up water from the sea.

NOTE 2.-Waterspouts sometimes discharge torrents of water.

NOTE 3.-Waterspouts are frequently small and harmless; but the wind with which they

structive force of the most violent tornadoes.

NOTE 4.-The MovING SAND PILLARS of the Arabian deserts are analogous in their nature to waterspouts.

NOTE 1.-If on every part of the earth's sur-are accompanied exerts, at other times, the deface the air were of the same density, there could be no such thing as wind, for the different parts of the atmosphere would balance each other, and, consequently, there could be no flowing of the air from one place to another. But suppose. that over a limited portion of the earth's surface the air should, from any cause, have its weight in the Chinese seas.

A TYPHOON is a violent hurricane

NOTE 1.-Hurricanes and typhoons are whirling storms having a diameter of from 50 to 500 miles.

NOTE 2.-The diameter of a tornado is small,

sometimes not exceeding a few hundred yards. NOTE 3.-The whirling movements of the air are supposed to be caused by electricity.

The TRADEWINDS are winds which prevail within the tropics, and blow in nearly the same direction throughout the year. In the northern hemisphere they blow from the northeast, and in the southern hemisphere, from the southeast.

The SIMOON OF SAMIEL is a hot, dry wind that blows occasionally in Arabia and the adjoining countries, and is caused by the extreme heat of the sandy deserts. (Arabic, samma, poisonous.)

NOTE. This wind often proves fatal to travel

ers who are overtaken by it.

The CHAMSIN is a hot wind that| blows in Egypt from April till June.

Flatulent, having the stomach dis tended with air.

Inflate, to puff up with air. Fig. To puff up with pride.

AER (L) and AEP [AER], (Gr.), air. Hence,

Aeriform, having the form of air. The various gasses are aeriform substances.

Aerate, to impregnate with carbonic acid which was formerly called fixed air:

Aeronaut, one who sails through the air. (G. vAUTns [nautes], a sailor.) Aeronautics, the art of sailing through the air.

Aerostat, a balloon. (Gr. TATOS [statos], balanced [in the air.])

Aerostatics, 1. The science which treats of the equilibrium of elastic fluids. 2. Aerial navigation.

Aerostation, aerial navigation. Aerolite, a stone which has fallen from the air. (Gr. os [lithos], a stone.) AIOHP [AITHER], the air. (Gr.)

The HARMATTAN is a wind similar to the simoon, blowing from the north-Hence,

ruary.

east over Senegambia and Guinea. It Ether, a thin, subtle matter, much occurs at intervals during the months finer and rarer than air, which, some of December, January, and Feb- philosophers suppose, begins from the limits of the atmosphere, and occupies the heavenly space. Ethereal, 1. Filled with ether; as, the ethereal, regions 2. Consisting ether or spirit.

The SIROCCO is a hot wind known in Italy and Sicily. It blows in the latter part of June, and during the month of July. It is supposed to originate in the sandy deserts of Africa.

of

Vast chain of being which from God began,
Natures ethereal, human, angel, man.-Pope.

VENTUS, wind. (L.) Hence, Ventilate, to expose to the free passage of air or wind,

The MONSOONS are periodical winds which prevail in the Indian ocean and in Hindoostan. From April to October they blow from the south- Vent, 1. A small opening in a cask west, and during the remainder of to admit air as the liquor runs out. the year, from the northeast. 2. Access of air to burning fuel. 3.

The ETESIAN WINDS are known in An outlet. Confined gas finds vent the eastern Mediterranean. Com-through a small orifice. Suppressed mencing toward the middle of July, emotion may find vent in words. they continue to blow about six Ventiduct, a pipe for the passage weeks from the northeast. They of wind or air in ventilating apartconsist of cooler and heavier air ments. (L. duco [ductum], to lead. pressing forward to displace the hot and rarefied air of the Sahara. (Gr. STHOLE [etesios], yearly; from eros [etos], a year.)

FLO [flatum], to blow. (L.) Hence,
FLATTER, to puff with empty praise.

ANEMOX [ANEMOS], the wind. (Gr.) Hence.

Anemometer, an instrument for measuring the force of the wind. (Gr. μerpe [metreo], to measure.)

Anemography, a description of the

force

1. General Ideas. GRAVITATION is the which causes masses and particles of all kinds of matter, when situ- the center of gravitation. ated apart, to have a tendency to move toward each other.

is the center of the earth, this being the point toward which bodies on all sides of the earth tend in falling.

DOWNWARD, in a direction toward

NOTE.-Gravitation is the cause of weight. Consequently, if this force did not exist, no mass of matter, however large and dense, could have any weight whatever. (L. gravis, heavy.)

Laws of Gravitation.

1. Different masses exert the gravitating force with an intensity which is proportional to the quantity of matter which they contain.

2. The gravitating force exerted by a particular mass diminishes as the square of the distance from the center of the mass increases.

Consequences of these Laws.

UPWARD, in a direction from the

center.

Low, situated near the center.
HIGH, remote from the center.
To FALL or DESCEND is to move
toward the center.

To RISE or ASCEND is to move from the center.

The BOTTOM or BASE is that part of a body which is nearest to the

center.

The TOP or SUMMIT is that part of a body which is farthest from the center.

PERPENDICULAR or UPRIGHT, situated in the direction of a line drawn through a given point directly toward or directly from the center.

1. If the earth, with its present density, had a diameter equal to that of Jupiter, the weight of all bodies at the surface would be increased elevenfold. A man who now weighs 150 pounds, would, in that case, weigh more than 1600 pounds, and would consequently be unable to move his own body. If, on the other hand, the diameter of the earth did not exceed that of the planet Vesta, water, in turning a wheel, would exert HORIZONTAL or LEVEL, situated in only 1-25 of its present mechanical force. A world much larger or much smaller than the the direction of any line drawn earth would, therefore, be an inconvenient habi-through a given point at right angles 2. At the distance of two semidiameters from to a line drawn through the same the earth's center, the weight of bodies would point toward the center.

tation for man.

be reduced to one-fourth of their weight at the surface; and at the distance of the moon, or 60 semidiameters, the weight of a body would be 3600 times less than at the surface.

3. If the surface of the earth were an infinite plain, the depth and density being uniform, the gravitating force would be the same at all dis

tances above the surface.

4. If the surface of the earth were an infinite plain, and if the depth were at the same time infinite, the weight of the smallest particle of matter would be infinite, and falling bodies would move with an infinite velocity.

The CENTER of GRAVITATION in any larger mass of matter is the point toward which small masses situated in the vicinity of the larger mass tend.

NOTE. The center of terrestrial gravitation

sense; as, a grave matter. 2. Characterized by soberness of looks or deportment, as if the mind were occupied with weighty matters.

Gravity, 1. Weight. 2. Soberness of countenance or deportment.

Grief, (from gravis), sorrow, because sorrow is something that bears heavily upon our feelings.

Grievance, an injury or wrong done by one person to another.

NOTE. The idea implied in this term is that of imposing an irksome burden.

Aggravate, lit, to increase the weight. Hence, to make worse or more severe; as, to aggravate a fault or a disease. (ad, to.)

PONDUS [ponderis], a weight. (L.) Hence,

Ponderous, heavy.

Ponder, to weigh in the mind. Imponderable, destitute of appreciable weight. Light, heat, and electricity are imponderable agents. (in, not.) ONUS [oneris], a burden. (L.) Hence,

Onerous, burdensome; as, onerous duties.

Exonerate, to free from a burden. (used only in a figurative sense; as to exonerate a person from blame.) LIGHT, possessing but little weight. LEVIS, light. (L.) Hence,

Levity, lightness, either in a literal or figurative sense. Hydrogen gas, on account of its great specific levity is used for inflating balloons. Levity of mind is a want of seriousness.

Alleviate, to lighten; as, to alleviate pain. (ad, to.)

TO WEIGH is to determine the weight of a quantity of matter.

A BALANCE is an instrument for weighing, consisting of two dishes called scales, the one for receiving the article to be weighed, and the other for receiving the weights. (L. bi, two, and lanx, a dish.)

A PAIR of SCALES is a balance.

parts of a body to balance each other. (Fr. poids, weight.)

Equipoise, equilibrium.

PENDO [pensum], to weigh. (L. from pendeo, to hang, since in weighing, the article is always suspended in some way.) From Pendo comes.

PENSO [pensatum], to try the weight frequently and carefully. (L.) From Pendo and Penso come the following English derivatives:

Pensive, lit., weighing in the mind. Hence, thoughtful with melancholy or sadness.

Pension, lit., a paying out of money by weight. Hence, a yearly allowance for past services.

Compensate, lit., to weigh out to a man the money due for trouble or services. Hence, to pay.

Recompense, lit., to weigh back. Hence, to reward. (re, back.)

Dispense, lit., to weigh out in small and separate parcels. Hence, to distribute; as, to dispense favors; to dispense justice. (dis, asunder.)

Dispensation, 1. The act of distributing. 2. A weighing out, by Divine Wisdom and Goodness, of laws, rites, and benefits, adapted to the existing condition of man; as, the Mosaic dispensation; the Christian dispensation.

and

Dispensary, a place in which medicines are dispensed to the medical advice is given gratis.

poor,

Dispensatory, a book giving directions in regard to the proportions in which the simple drugs are to be weighed out in compounding medicines.

Expend, lit., to weigh out. Hence, to lay out money. (ex, out.) Expense, money laid out. Expenditure, the act of laying out money.

Spend, an abbreviation of Expend. Prepense, lit., weighed beforehand. Hence, Premeditated; as, malice

LIBRA, a pair of scales. (L.) prepense. (pre, beforehand.) Hence,

Equilibrium, a mutual balancing

3. Low.

of two weights. (L. aequus, equal.) LOWLY, 1. Low in regard to rank To POISE is to cause two opposite and distinction; as, the lowly poor.

2. Having a low estimation of one's ion of one's self, along with a conown worth. temptous opinion of others. (Fr., haut, high.

7. Perpendicular.

A PERPENDICULAR direction is

indicated by the position which a string assumes when stretched by a weight attached to one end, while the other end is fastened to a fixed point. (L., per, through; and pena deo, to hang.)