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The Scian and the Teian muse,
The hero's harp, the lover's lute,
Their place of birth alone is mute
And Marathon looks on the sea;
I dreamed that Greece might still be free; For standing on the Persian's grave, I could not deem myself a slave. A king sate on the rocky brow
Which looks o'er sea-born Salamis; And ships, by thousands, lay below,
And men in nations;—all were his ! He counted them at break of dayAnd when the sun set where were they? And where are they ? and where art thou,
My country ? On thy voiceless shore
The heroic bosom beats no more!
Though linked among a fettered race,
Even as I sing, suffuse my face;
Must we but blush ?-Our fathers bled. Earth! render back from out thy breast
A remnant of our Spartan dead!
What, silent still ? and silent all ?
Ah! no; the voices of the dead
And answer, “Let one living head,
Fill high the cup with Samian wine!
And shed the blood of Scio's vine!
Where is the Pyrrhic phalanx gone?
The nobler and the manlier one ? You have the letters Cadmus gave Think ye he meant them for a slave ? Fill high the bowl with Samian wine!
We will not think of themes like these! It made Anacreon's song divine:
He served—but served Polycrates-
Was freedom's best and bravest friend; That tyrant was Miltiades!
Oh! that the present hour would lend Another despot of the kind! Such chains as his were sure to bind. Fill high the bowl with Samian wine!
On Suli's rock, and Parga's shore, Exists the remnant of a line
Such as the Doric mothers boro; And there, perhaps, some seed is sown, The Heracleidan blood might own.
Trust not for freedom to the Franks
They have a king who buys and sells!
The only hope of courage dwells;
Our virgins dance beneath the shade
But gazing on each glowing maid,
Where nothing, save the waves and I,
There, swan-like, let me sing and die:
Echo, (G.) a reflected sound.
| Pendulum, (pendeo, L.) a vibrating body Gamut, (from the Greek letter gamma) suspended from a fixed point, as in a the musical scale.
clock, Medium, (L.) the substance by which Propagate, (propago, L.) to spread;
sound, light, heat, &c., are trans when applied to light, sound, &c., it mitted from one point to another. means to impel, or move forward in Plural, mediums or media.
space, and at the same time to multiOctave, (octavus, L.) an eighth, or mu ply by successive production. Hence
sical interval of seven degrees, and propagation,
Vibrate, (vibro, L.) to swing: to move Oscillate, loscillo, L.) to swing, or move this way and that, to oscillate. Hence
backwards and forwards. Hence also vibratory and vibration, oscillation.
SOUND-WAVES, AND THEIR PROPAGATION. THERE are few things so apt to deceive us as the motion of waves. When we stand upon the sea-shore, and look beyond the line of breakers at our feet, we see wave behind wave, far as the eye can reach, all of them manifestly advancing towards us. It seems as if the sea were gradually
yond thear as the eye cat seems as
flowing in upon the land. If the tide is advancing, this may be so far in accordance with fact, but the appearance is quite the same even when the tide is receding. It must therefore be a deception. Take another case of wave motion, that of a field of standing corn agitated by the wind. Every one who has been in the country on a windy day in summer must have noticed how waves, not unlike those of the sea, travel visibly over such a field in the direction in which the wind blows. Yet we know that the stalks of corn are not carried out of their places. Each stalk stoops in succession as the wind passes over it, and then recovers itself, partly by its own strength, and partly by the reaction of the other stalks which it strikes. The ears meanwhile go and return with a sort of vibratory or alternate motion. Once more, look what happens when a stone is thrown into a pool. Immediately circular waves, proceeding from the stone as a centre, spread in every direction, each gradually increasing in diameter as it goes. Yet the surface does not become hollow at the point from which all the waves are moving. The fact is, that it is the waves alone which have a progressive motion, the water composing them, like the stalks and ears of corn, has only a vibratory or alternate motion. It simply moves up and down. The same thing is true of the sea itself. The waves move towards the land, the water of which they are formed does not.
In every substance which is elastic, whether solid, liquid, or gaseous, the particles may be thrown into a kind of vibratory motion, similar to the motion of waves. If any part of such a body is compressed, as when a bell is struck by its clapper, the elasticity of the compressed particles urges them to expand again, and by their expansion the force of the blow is conveyed to the surrounding parts. By these the process is repeated, and the impulse transmitted to a still wider circle. Thus the motion spreads in every direction, as the waves do in a pool into which a stone has fallen. But this is not all. The elastic force called into action by compression, does more than restore the compressed parts to their former dimensions. When a pendulum
hanging at rest is drawn to one side and let go, it does not simply return to its position of rest, and there suddenly stop. The reason is obvious. Being in motion when it arrives at that position it cannot stop of its own accord, and therefore goes towards the other side, till gravity first stops it, and then pulls it back. Thus it continues to oscillate from one side to the other. Exactly in the same way, the elasticity of a compressed substance tends to produce oscillation. Compression is succeeded by undue dilatation, to be followed again by compression, then again by dilatation, and so on. Hence the motion caused by striking an elastic body, is a vibratory motion consisting of alternate compressions and dilatations, and propagated in every direction after the manner of waves. Now here is the point which, from its importance, demands special attention. It is this vibratory, wavy motion which gives us the sensation of Sound.
How the motion becomes a sensation no man can tell; it is one of the mysteries of life, known to God only. Even the structure of the ear, the mere instrument in this strange transformation, is not well understood. But this we do know, that unless some vibrating substance, or medium, is in contact with the ear, no sound will be heard. The most common medium of sound is atmospheric air. We have already learned that a bell struck in a vacuum gives no sound.
Waves of sound are propagated at different rates through different substances. In air, they travel faster or slower according to the temperature, but the usual rate is about 1120 feet per second, or more than 12 miles in a minute. When a gun is fired, the flash and the report are really simultaneous, and to a person standing close by they appear to be so. But a person at a distance sees the flash a considerable time before he hears the report. Light travels so very fast, that we may suppose it to pass instantaneously from the gun to the eye of the spectator, even though he be several miles away. Sound, however, goes more slowly, taking one second for every 1120 feet it has to travel. If, therefore, we reckon 1120 fect for every second after we