No human hand could, for any length of time, make a body move regularly backwards and forwards; but in a clock the pendulum swings steadily day and night, performing its oscillations with invariable regularity, and marking for us the progress of the hours. And-to name but one other instance -think of the way in which a reserve of motive force is laid up in a watch, and given regularly off as it is required! So happily constructed and nicely attached to the other parts of the watch is the spring, that a few seconds expended in turning the key keeps the machinery going for twentyfour hours, without any further interference on our part.

In these and manifold other ways does machinery assist human power. But muscular strength is only one of the forces which is made available by the intervention of machinery. The wind, the running stream, the expansive force of steam, and other giant forces of nature are similarly made our servants; and through them we acquire powers of labour and production, far greater than all human strength combined could supply. Compiled.

THE MECHANICAL POWERS.

EVERY machine or engine, however complicated, will be found, on examination, to be made up of two or more simple machines combined together. These simple machines, which are called the mechanical powers, are six in number, and have the following names,-the Lever, the Wheel and Axle, the Pulley, the Inclined Plane, the Wedge, and the Screw.

Every one has seen men raising a stone by means of a bar of iron. This bar is a Lever. In this machine three

things are to be considered, the power or force which presses on it, the weight to be raised, and the prop on which

it rests. The advantage gained results from having the power which presses much farther from the prop than the weight to be raised. If the distance of the power from the prop be four times as great as the distance of the weight, the advantage will be as 4 to 1. If the distance be six times as great, the advantage will be as 6 to 1; and, generally, the power bears to the weight an inverse ratio to the arms of the lever. Levers are of three kinds :-First, when the prop is between the weight and the power;-Second, when the weight is between the prop and the power;-Third, when the power is between the weight and the prop. It is by a lever of the first kind that a seaman moves his rudder and a blacksmith his bellows. Gates and doors are levers of the second kind-the hinge being the prop on which they move. A spade and a pitchfork for raising hay are instances of levers of the third kind.

In the Wheel and Axle, a weight is raised by means of a rope coiling round the axle,

while the power is applied to the outer rim of the wheel. The advantage gained is in proportion to the extent by which the width or diameter of the wheel exceeds that of the axle. The semi-diameter of the wheel, and the semi

diameter of the axle, may be considered as levers of which the centre is the common prop. An equilibrium will be produced when the power is to the weight as the semidiameter of the axle is to the semi-diameter of the wheel, or as the circumference of the axle is to the circumference of the wheel. In raising weights with this machine the rope coils round the axle and enlarges the diameter; hence the advantage of the power is continually diminishing; and, accordingly, in raising a bucket from a deep well the weight is felt much more sensibly as it approaches the top. We have examples of the wheel and axle in the crane used on wharfs and quays for drawing goods up from a ship, and in the capstan for lifting the anchor.

The Pulley is used principally in hoisting the sails of ships. A single pulley gives no mechanical advantage, but it is of use in altering the direction in which a force may be applied. If two pulleys be used, the power will keep in equilibrio a weight double its own; if three be used, the power will

balance three times as much, and so on. In this machine the advantage is greatly diminished by the friction of the axles and the want of pliancy in the ropes. It may be regarded, as to principle, either as a modification of the lever, or as a distinct mechanical power.

The Inclined Plane is used to facilitate the raising of great weights. It is evident

ly much easier to roll a

cask along a plank into a waggon than to raise it from the ground. In the inclined plane, an

equilibrium is produced when the power is to the weight as the height of the plane is to the length of its sloping side; but as the friction in the use of this machine is very great, a much less power than that deduced by calculation will keep a body in equilibrio, and a much greater power will be requisite to draw it upwards.

In the Wedge the law of equilibrium is, that the power should be to the weight as half the length of the back is to the length of one of the sides; but, on account of friction and other causes, no law can be stated as universally accurate. In real practice, all that we can say is, that the less the breadth of the back in proportion

to the length of the side, the greater is the advantage.

Nature, whose works uniformly display the utmost wisdom in their design, has formed the beaks of birds wedge-shaped, for the purpose of enabling them to dig into the ground, etc. The figure of a bird, too, is similarly fitted for cleaving the air, as is the breastbone of a waterfowl for making way through the water; and the shape of boats and ships may, perhaps, have been first suggested by the shape of these animals. A grand military evolution of the ancients was forming a battalion into the shape of a wedge; and many instances occur in history of an enemy's line having been broken by this contrivance.

The principle of the Screw is the same as that of the inclined plane. The weight, instead of proceeding straight forward, moves in a spiral direction, gradually ascending to the top; and the equilibrium is calculated in the same manner as in the inclined plane. Compiled.

QUOTATIONS FROM BYRON.
Greece.

HE who hath bent him o'er the dead
Ere the first day of death is fled,
(Before Decay's effacing fingers

Have swept the lines where beauty lingers),
And marked the mild angelic air,

The rapture of repose that's there,—

He still might doubt the tyrant's power;

So fair, so calm, so softly sealed,

The first, last look by death revealed!
Such is the aspect of this shore;
'Tis Greece, but living Greece no more!
So coldly sweet, so deadly fair,
We start, for soul is wanting there.

Clime of the unforgotten brave!

Whose land from plain to mountain-cave
Was Freedom's home or Glory's grave!
Shrine of the mighty! can it be,
That this is all remains of thee?

Approach, thou craven crouching slave:

Say, is not this Thermopyla?

These waters blue that round you lave,-
Oh servile offspring of the free,
Pronounce what sea, what shore is this?
The gulf, the rock of Salamis !

These scenes-their story not unknown---
Arise, and make again your own;
Snatch from the ashes of your sires
The embers of their former fires;
And he who in the strife expires
Will add to theirs a name of fear,
That Tyranny shall quake to hear,
And leave his sons a hope, a fame,
They, too, will rather die than shame :
For Freedom's battle once begun,
Bequeathed by bleeding Sire to Son,
Though baffled oft is ever won.

Rome.

THE Niobe of nations! there she stands,
Childless and crownless, in her voiceless woe;
An empty urn within her withered hands,
Whose holy dust was scattered long ago;
The Scipios' tomb contains no ashes now;
The very sepulchres lie tenantless

Of their heroic dwellers: dost thou flow,
Old Tiber! through a marble wilderness?
Rise, with thy yellow waves, and mantle her distress.

Thunder-Storm among the Alps.

THE sky is changed!—and such a change! Oh night, And storm, and darkness, ye are wondrous strong, Yet lovely in your strength, as is the light

Of a dark eye in woman! Far along,

From peak to peak, the rattling crags among Leaps the live thunder! Not from one lone cloud, But every mountain now hath found a tongue, And Jura answers, through her misty shroud, Back to the joyous Alps, who call to her aloud! And this is in the night :-Most glorious night! Thou wert not sent for slumber! let me be