second night was in direct opposition to the existing economy of nature.

Differences of colour in bodies, of roughness or smoothness, of coarseness or fineness of texture, as well as differences of substances, are sufficient, however, to produce essential differences between them in this respect. Now, the leaves of no two descriptions of plants have surfaces precisely of the same colour, smoothness, and dryness; no two, therefore, radiate heat precisely alike, and no two attract equal depositions of dew. Thus, not only is it ordered, by a wonderful provision, that the atmosphere should temper the heat to every plant, but that, in the season of drought, it should water it at eventide and in the morning; and water each, as it were, with a different hand, and a different abundance. Who shall doubt that this varying abundance is proportioned to the thirst of each.-Moseley.

LESSON XVII.-TUESDAY.

FORCE.

Force is that which produces or tends to produce motion. or change of motion in bodies. Motion is change of position in space, and occupies time. The space moved through, compared with the time, is the velocity of a body; and its momentum is the velocity multiplied into its weight. Hence the momentum of a body weighing four pounds, and moving at the rate of three miles per hour, is equal to that of a body weighing two pounds, and moving at the rate of six miles per hour.

A body moving in a straight line is said to have rectilinear motion; moving in a curved line, its motion is termed curvilinear. If it moves backwards and forwards, as a pendulum, it is said to have vibratory or oscillating motion. Motion on an axis, as a pulley, is termed rotatory. Motion from one place to another is called motion of translation. Simple motion is produced by a single force; compound motion, by more than one force. If a person travelling on a railway moves from one side of the carriage to the other while the train is proceeding, he moves at the same time across the carriage and onwards with the train. The motion across

the carriage is produced by his own muscular force, while that onwards is occasioned by the engine. These two forces produce the compound motion of which he partakes. A stone dropped from the carriage does not fall perpendicularly. Its falling motion is compounded with that of the carriage, and it goes downwards and onwards at the same time, moving towards the ground in a slanting direction. Strictly speaking, we never see any instances of simple motion. The earth itself has a compound motion, resulting from its rotatory motion on its axis, and its motion of translation in its orbit ; and hence bodies moving on the surface of the earth or in the atmosphere partake of these two motions in addition to their own.

Attractive forces tend to draw bodies together; repulsive forces tend to separate them. The forces of attraction are cohesion, chemical affinity, capillary attraction, and gravity.

Cohesion acts on similar molecules of matter. The molecules of a piece of sulphur are held together by this force. Chemical attraction acts on dissimilar molecules of matter. Sulphide of iron is composed of sulphur and iron, the particles of the one being united to the particles of the other by chemical attraction. Capillary attraction is manifested by bodies of a porous nature; and only affects liquid substances. Water, by capillary attraction, is drawn up into sponge, or a piece of sugar. Glass tubes, with very small diameters, produce the same effect, and are called capillary tubes. These three forces cease to act when the bodies affected by them are separated from each other by inappreciably small spaces. They are therefore said to act only at insensible distances.

The force of gravitation is, as far as we know, absolutely universal, acting at all distances, and on all bodies, whether molecules or masses. It is this force which causes bodies to fall to the earth. The law of gravity may be stated thus:— Gravity is directly proportional to the quantity of matter in bodies, and inversely as the square of their distance. The wind, the tides, and the flow of rivers are all, directly or indirectly, dependent on the force of gravity.

A force increasing the velocity of a body every successive instant is termed accelerating force, and that which diminishes

the velocity of a body every successive instant, is termed retarding force. If such increase or diminution be regular, the force is called uniformly accelerating, or uniformly retarding; but if the increase or diminution be irregular, the force is called variable accelerating, or variable retarding. A stone thrown perpendicularly from the ground to a height of 144 feet, occupies six seconds of time before it returns to the ground; three in its ascent, and three in its descent. During its ascent it rises 80 feet the first second, 48 feet the second second, and 16 feet the third second. It then begins to descend. During the first second occupied in its descent it falls 16 feet, 48 feet in the second second, and 80 feet in the third second. As it ascends its velocity is diminished by 16 feet per second, and increased at the same rate during its descent. Gravity is the cause of both these changes, and acts as a uniformly retarding force during the ascent, and as a uniformly accelerating force during the descent.

Force does not always produce motion in bodies. A weight suspended by a string, so that it does not move, is nevertheless acted on by two forces, viz., gravity, and the tension of the string. Each of these forces tends to produce motion in the weight, but they tend to move it in opposite directions, and, being equal, counterbalance each other's effect, and hence no motion ensues. When a body acted on by two or more forces does not move, it is said to be in equilibrium; when neither in motion, nor under the influence of force, it is said to be at rest. Rest and equilibrium are both opposed to motion, but are distinguished from each other. The latter implies the action of force.

LESSON XVIII.-WEDNESDAY.

COMMERCE.

The band of commerce was designed
To associate all the branches of mankind;
And if a boundless plenty be the robe,
Trade is the golden girdle of the globe.
Wise to promote whatever end He means,
God opens fruitful Nature's various scenes:

Each climate needs what other climes produce,
And offers something to the general use;
No land but listens to the common call,
And in return receives supply from all.
This genial intercourse, and mutual aid,
Cheers what were else a universal shade,
Calls nature from her ivy-mantled den,
And softens human rock-work into men.
Ingenious Art, with her expressive face,
Steps forth to fashion and refine the race;
Not only fills necessity's demand,
But overcharges her capacious hand:
Capricious taste itself can crave no more
Than she supplies from her abounding store:
She strikes out all that luxury can ask,
And gains new vigour at her endless task.
Her's is the spacious arch, the shapely spire,
The painter's pencil, and the poet's lyre;
From her the canvas borrows light and shade,
And verse, more lasting, hues that never fade.
She guides the finger o'er the dancing keys,
Gives difficulty all the grace of ease,
And pours a torrent of sweet notes around,
Fast as the thirsting ear can drink the sound.
These are the gifts of art; and art thrives most,
Where Commerce has enrich'd the busy coast;
He catches all improvements in his flight,
Spreads foreign wonders in his country's sight;
Imports what others have invented well,
And stirs his own to match them, or excel.
'Tis thus, reciprocating each with each,
Alternately the nations learn and teach;
While Providence enjoins to every soul
A union with the vast terraqueous whole.
Heaven speed the canvas, gallantly unfurl'd
To furnish and accommodate a world,
To give the pole the produce of the sun,
And knit the unsocial climates into one.
Soft airs and gentle heavings of the wave
Impel the fleet, whose errand is to save,

To succour wasted regions, and replace
The smile of opulence in sorrow's face.
Let nothing adverse, nothing unforeseen,
Impede the bark that ploughs the deep serene,
Charged with a freight transcending in its worth
The gems of India, Nature's rarest birth;
That flies, like Gabriel on his Lord's commands,
A herald of God's love to pagan lands.-Cowper.

LESSON XIX.-THURSDAY.

ENGLISH HISTORY-THE NORMAN LINE.

The battle of Hastings determined the succession to the English throne. William the Conqueror was crowned at Westminster, on the 25th of Dec. of the same year, 1066. His government was at first moderate. He contented himself with confiscating the estates of those who had fought against him at Hastings, and bestowing them upon his own followers. His first absence in Normandy was, however, the signal for rebellion, into which the English were driven by the oppressions of their new rulers. William returned in the middle of winter, repressed the rising, and punished the rebels with severity. Successive insurrections were attended with similar results, until the greater part of the land, and all offices of trust and authority, were transferred into the hands of the Normans. The greater part of the Saxon nobles had either fallen in the field, or had been despoiled of their possessions, large numbers of the common people had perished by violence or famine, and the remainder at length submitted to the tyranny which they could not escape. It was not until after seven years of brave, though ineffectual struggles on the part of the English, and of cruel exterminating war on that of the invaders, that the conquest of England was completed.

William was a prince of great ability-brave, sagacious, and circumspect; but he was also haughty, crafty, cruel, and unscrupulous. His passion for the chase was excessive; he laid waste great part of Hampshire, destroying villages and churches, and rendering the inhabitants homeless fugi