“Prince Leopold’s voice is of very fine tone, and gentle; and its articulation exceedingly clear, accurate, and impressive, without the slightest affectation.  You know that sort of reasoning emphasis of manner with which the tongue conveys whatever deeply interests the mind.  His ’My Charlotte!’ is affecting; he does not pronounce it as ‘Me Charlotte,’ but very simply and evenly, ‘My Charlotte.’”

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NOTES OF A READER.

KNOWLEDGE FOR THE PEOPLE.

Part VII.—­Mechanics.

We quote a few articles from the Introductory portion, illustrating the general principles of Mechanical agencies.

Why are we said to know of nothing which is absolutely at rest?

Because the earth is whirling round its axis, and round the sun; the sun is moving round his axis, and round the centre of gravity of the solar system; and, doubtless, round some more remote centre in the great universe, carrying all his planets and comets about his path.  One of the grand laws of nature is, that all bodies persevere in their present state, whether of motion or rest, unless disturbed by some foreign power.  Motion, therefore, once began, would be continued for ever, were it to meet with no interruption from external causes, such as the power of gravity, the resistance of the medium, &c.  Dr. Arnott adduces several familiar illustrations of motions and forces.  Thus, all falling and pressing bodies exhibit attraction in its simplest form. Repulsion is instanced in explosion, steam, the action of springs, &c.  Explosion of gunpowder is repulsion among the particles when assuming the form of air.  Steam, by the repulsion among its particles, moves the piston of the steam-engine.  All elasticity, as seen in springs, collision, &c. belongs chiefly to repulsion.  A spring is often, as it were, a reservoir of force, kept ready charged for a purpose; as when a gun-lock is cocked, a watch wound up, &c.

Why does a billiard ball stop when it strikes directly another ball of equal size, and the second ball proceed with the whole velocity which the first had?

Because the action which imparts the new motion is equal to the re-action which destroys the old.  Although the transference of motion, in such a case, seems to be instantaneous, the change is really progressive, and is as follows:—­The approaching ball, at a certain point of time, has just given half of its motion to the other equal ball; and if both were of soft clay, they would then proceed together with half the original velocity; but, as they are elastic, the touching parts at the moment supposed, are compressed like a spring between the balls; and by their expanding, and exerting force equally both ways, they double the velocity of the foremost ball, and destroy altogether the motion in the other.

Why does a walking stick help a man on a journey?