shells, shell within shell, as we see in the coats of an onion."

Of the Velocity of Sound. "Corrected by the experiments of various observers, the velocity of any impression transinitted by the common air may, upon an average, be reckoned 11,300 feet in a second."

"M. Biott, whose attention is ever alert, has seized an occasion of considerable improvements now going forward in the capital of France, to repeat, with great precision, experiments similar to those proposed by the ingenious Chiadni, to determine the swiftness of sound through a solid body."

The pipes intended to convey water to Paris consist of cylinders of cast iron, each eight feet-three inches in length; the joints are secured by a collar of lead, nearly half an inch 'thick, covered with pitched cotton rag, and strongly compressed by screws. Into one end of the compound pipe was introduced an iron hoop, holding a bell with a clapper; and at the other end, the observer was stationed. On striking the clapper at once against the bell and the inside of the tube, two distinct sounds were heard at the remote extremity, the one sent through the iron, and the other conducted along the air. The interval between these two sounds was measured by a chronometer that marked half-seconds. In one experiment, the assemblage of pipes, including the leaden joints, extended to 2550 feet, or nearly half a mile and on a medium of 200 trials the two sounds were heard at the interval of 2-79 seconds. The time the sound would take, according to the calculation, to travel the same distance through the air is 2.5 seconds: whence the difference 29" marks the time of conveyance along combined tubes. From numerous combined trials, M. Biott concludes, that the true quantity was 26"; and therefore that sound is transmitted ten or twelve times faster through cast iron than through the atmosphere."

Wunck, on the velocity of sound in wood, informs us, "that a sound was conveyed instantaneously through 36 connected laths of 24 feet each, or 864 feet, if not through 72, which was the whole number employed: 72 laths of 24 feet would equal 1728 feet."

Count Giordano Riccati, in his work on strings and elastic fibres, has proved, that sound passes through a space filled with air, of a given length, in the same time that a column of air of the same length, contained in an organ-pipe open at both ends, makes one vibration.

An open organ-pipe of 10 feet makes 100 vibrations in a second. Air inadequate to the Phenomena of Sounds.

"It seems a question," says Mr. Jones, "more arduous than is commonly supposed, by what means sound is propagated. Natural Philosophy has commonly taught that air is the vehicle of sound; but, if sound goes where no air can convey it, through the most solid bodies, and that with the greatest ease, some other cause besides, the air must concur. The slightest scratching at one end of the largest piece of timber is heard very distinctly when the ear is applied to the other end, though it cannot be heard at half the distance when we use the air as the vehicle. This must be owing to the intervention of some cause more moveable and more powerful than the air itself. If it be supposed that the particles of wood, which are in contact with the pin's point, give motion to those that lie next them, and so on, till the vibration reaches to the other extremity; the cause is not adequate. It is therefore much easier to conceive that the effect arises from the vibrations of a medium within the pores,. easily agitated, and communicating its pulses to any distance, rather than from the action of the solid parts upon one another. Then will this occult communication of sound be similar, in some degree, to the passage of the electric ether; which goes with difficulty through the air, but fics instantly through the pores of solid bodies *."

Through fir-wood sound passes 17,400 feet, or more than three miles, in a secoud. Mr. Chladni tells us that the kinds of wood he examined would conduct sound about 11,000 to nearly 18,000, and burnt pipe and clay from 10,000 to 12,000 feet in a second.

* La Marck, on the medium of sound, thinks it a medium more subtle than air. I have had no opportunity of consulting his observations. Jour. Phy. XLIX. 397.

Derham

Derham argues, that as sound moves near 1200 feet in a second, and the most violent wind not more than 60 miles in an hour, which is at the rate of 88 feet in a second; the particles of air which communicate the sound must be more subtle than those which constitute wind. If wind acts by the grosser parts of air, and sound by the finer, this may be a reason why they do not interfere, nor disturb one another's motions.

The velocity of sound to a brisk wind is as fifty to one.

Sound describes equal spaces in equal times. Derham has proved, by experiment, that all sounds whatever travel at the same rate. The sound of a gun, and the stroke of a hammer, are equally swift in their motions. The softest whisper flies as swiftly, as far as it goes, as the loudest thunder.

Of Hearing under Water.

I shall enliven this article with a merry story from Lord Bacon. "Let a man go into a bath, with a tub over his head; let him speak, and any that shall stand without shall hear his voice plainly, but yet extremely sharp and exile (thin), like the voice of puppets; but yet the articulate sounds of the words would not be confounded. A man might think that the Sicilian poet had knowledge of this experiment: for he saith, that Hercules' page, Hylas, went with a waterpot to fill at a pleasant fountain that was near, and that the nymphs fell in love with the boy; and that Hercules, ruissing his page, called him by his name aloud that all the shore rang of it; and that Hylas, from within, answered his master but with so small and exile a voice, as Hercules thought he had been three miles off, when the fountain, indeed, was fast by."

Sound is propagated through water with the velocity of 4900 feet in a second. N. B. An English mile is 5280 feet.

Two stones being struck together under water, may be heard at a much greater distance by an ear under water in the river, than it can be heard through the air; Dr. Franklin thinks he has heard it a mile."

Professor Robison informs us that he heard the sound of a bell, transmitted by water, at the distance of 1200 feet. Mr. Canton has ascertained that the elasticity of water is about 22,000 times as great as that of air;

which will give velocity of 49,000 feet in a second.

"The sound of a bell," says Derham, "under water, is much duller and not so loud; and it is also a 4th deeper."

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Of the Divergence of Sound. "It has generally been asserted," says Dr. Young, chiefly on the authority of Newton, that if any sound be admitted through an aperture into a chamber, it will diverge from that aperture, equally, in all directions. This, however, appears not to be the fact. It is well known, that if a person calls to another with a speaking trumpet, he points it towards the place where the hearer stands. i am assured by a very respectable member of the Royal Society, and indeed it was long ago observed by Grimaldi, that the report of a cannon appears many times louder to a person towards whom it is fired, than to one placed in a contrary direction. It inust have occurred to every one's observation, that a sound, such as that of a mill, or fall of water, has appeared much louder after turning a corner, when the house or other obstacle no longer intervened.”

Of Loudness of Sound.

This depends on the force with which the particles of air strike the ear. Why this loudness does not increase in arithmetical proportion we know not. But of this we are certain: that four equal voices, or four violins of equal power, are not four times as loud, as one voice, or one violin. Had the fact been otherwise,☛ the performances at Westminster Abbey, at Mr. Handel's commemoration, in one of which more than 600 were employed, would have stunned the audience.

The following passage relative to the accuracy of the organ of hearing, in distinguishing the difference of sounds nearly equal in force, is extremely curious and interesting.

"The waat of a sure method of measuring the momentum of the air when agitated by a vibrating body, with the same certainty with which the angles between rays of light are measured, appears to be the reason why the accuracy in question is so generally overlooked. But, though it seems very difficult to give a general rule for measuring magnitudes of this description, the following expe

riment