HAD an opportunity, during the

last summer, of visiting the fine monastic ruins of Rievaulx in Yorkshire, and can bear testimony to the accuracy of the description given in the Supplement to the First Part of your Vol. LXXX. I beg leave to send you a Drawing, representing the North-east View of the Abbey. Yours, &c.

TAKE the earliest opportunity of correcting a preliminary error in my last communication; which does not, however, render it less intrinsically valuable.

The Letter of Bp. Atterbury had been printed in the (now very scarce) Fifth Volume of that learned Prelate's Epistolary Correspondence, 1798," p. 175. Mr. Taylor, to whom it is addressed, was Clerk to Bridewell Hospital; and was the Bishop's Solicitor at his Trial. The request was in itself so reasonable, that the Government would scarcely have refused it; but the death of the Bishop, in the February following, put an end to the negotiation. The estate was at Great Houghton in Northamptonshire; and worth 400/. a year. It was afterwards claimed and obtained by the Bishop's son; by whom it was disposed of previous to his entering into orders, and obtaining the rectory of Oxhill in Warwickshire.

At Stourhead is a fine picture of the Prophet Elijah raising the dead Child to life, by Rembrandt, which was given to Mr. Hoare by Bishop Atterbury. It has been engraved by

Earlom.

A Series of Letters on AcOUSTICS, addressed to Mr. ALEXANDER, Durham Place, West Hackney.

T

HE following Letter will contain Observations on the Nature and Causes of Sound; the best I have been able to collect from a variety of authors.

"Sound is the cause of sensation we experience, when certain bodies called sanorous bodies vibrate, and communicate their tremulous motions to the atmosphere around us, or to GENT. MAG. February, 1812.

any other body in contact with our The ear, being affected by this motion, transmits the impression to the brain. In this manner we exercise the sense of hearing."

"Upon examining the organs of hearing," says Mr. Cuvier, in all animals in which that sense has been discovered, the only part constantly existing is a gelatinous pulp, which is covered by a fine elastic membrane, and in which the ramifications of the auditory are lost this pulp fills the labyrinth in all species from man to the cuttle-fish."

"We may form a véry natural idea of the connexion of this substance with the external movements which are the cause of sound: this quivering jelly will receive, with facility, the concussion transmitted to it by the vibrations of sonorous bodies, and communicate them to the brain. Thus far the motion can be traced : but the process which is afterwards necessary to produce perception escapes the anatomist as well as the metaphysician."

Of Sound in general.

"All sound, then, is made by motion, by some body being struck, and communicating its tremulous motions to the air. That sound may be propagated and carried on to a distance, it requires a medium to pass; and this medium is, in general, the air."

"Sound, when it meets with no obstacle, passes in a sphere; of which the sonorous body is at the centre."

This may be made plainer by the following illustration. Let us suppose a sonorous body in a state of vibration, and causing particles of air to vibrate; the body itself no bigger than a pea, and aloit in the air: and the particles of air adjacent to the sonorous body communicating their motion to the adjacent particles, till the whole particles in motion were equal to a giobe of a mile diame ter; then would the sound be heard, in every direction, at the distance of half the diameter, that is, half a mile from the centre of the sonorous body, represented by the pea.

"Sound is driven, in all directions," says Mr. Adams, "backwards and forwards, upwards and downwards, and on every side: the pulses go on succeeding each other, but one without outside the other in concentric shells,

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 transmitted 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 Chladni, 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 leadeu 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 ortwelve 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."

The

"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. 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 flies instantly through the pores of

solid bodies *."

Through fir-wood sound passes 17,400 feet, or more than three miles, in a second. 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."

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 must 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 want 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 proves, in a very satisfactory manner, what a delicate faculty the sense of hearing is. A bolt, driven by a spring against a fixed piece of metal, may be made to produce a succession of strokes of equal force; consequently, the concussion given to the air will also be equal; and will therefore occasion like effects on the same ear, placed at equal distances from the spring, the state of the wind and weather being the same in both cases. I caused an instrument of the preceding description to be struck repeatedly at the distance of 40 feet from my ear, care being taken to place it in the axis of hearing produced: after which, it was moved again in the same right line sometimes two feet further from me, and at other times two feet nearer my person; and I could always distinguish the distances varied. The range of the sound, at the distance at which it ceased to be audible, was 240 feet, or six times the interval made use of in the experiment. The sound which I employed was, therefore, of a moderate force; and perhaps the interval was a suitable one, being neither too great nor too small a part of the whole range. It appears then, that a good ear will discover a perceptible difference in the force of two equal sounds, the one of which moves through one sixth part of its whole range, and the other through a space which differs from the distance of the former only the 120th part of the range common to both.

"The foregoing i stance affords a remarkable proof of the ear's accuracy in comparing slight variations of sound: and I have reason to believe that the delicacy of my organs, in this respect, surpasses the medium of sensibility; for some ears, which were tried in the same manner, did not perceive the effects in question, until the instrument had been removed four feet, or the 6th part of my range. But either instance furnishes a proof sufficient for the present purpose, and shews the human ear to be a very delicate judge of comparative loudness." Manchester Memoirs, Vol. V. Part II. p. 687.

I should inform you, Sir, that Mr. Gough is blind; but need not make a common-place observation on that subject.

"The late blind Justice Fielding,"

says Dr. Darwin, "walked for the first time into my room, when he once visited me, and after speaking a few words, said, this room is about 22 feet long, 18 wide, and 12 high; all which he guessed by the ear with great accuracy." of the Intensity of Sound in different Fluids, from M. PEROLLE.

“Exp. VI. I closed all the joints of my watch with soft wax, and then suspended it by a silk thread. In this state I hung it by an iron brauch placed in the wall, so that the watch remained suspended in the middle of a glass vessel, five inches in diameter, and seven inches high, taking care that neither the watch nor the thread touched the vessel in any part. I remarked the kind of sound afforded by the watch, and the distance at which I ceased to hear it: after having marked this point, I then filled the vessel with water, into which I again suffered the watch to descend with the same precaution, of not suffering it or the thread to touch the vessel.

"The tone (timbre, quality of tone) was changed in the watch in a striking manner. The sound was propagated in so lively a manner that the glass, and a small table of wood, on which it stood, at a distance from the wall, seemed to undergo direct percussions from a solid body. But that which appeared the most astonishing was, that in the midst of all these agitations, the fluid, in which the watch was plunged, was perfectly tranquil, and its surface not in the slightest degree agitated.

"By substituting different liquids in the place of water, I had results in general analogous to those I had obtained with that fluid; but each of them gave a different modification to the sound, of which the intensity was noted as follows:

"Intensity of Sound observed in different fluids.

1. In air, serving as the term
of comparison, it ceased
to be heard at the dis-
tance of

2. In water, as that of ....
3. Oil-olive

...

..

..

8 feet.

20

16

21

4. Oil of Turpentine ...... 14 5. Spirit of Wine "It is proper to observe, that in repeating these trials I observed some variations in the intensity, which appeared

peared to depend on the organ of sense, or accidental noises.

"From the experiments made upon liquids it follows:

1. That these, as well as solids, do transmit sounds much better than the air, and that even the fat oils are not to be excepted.

2. That each fluid, upon trial, is found to modify the sound in a peculiar manner.

3. Philosophers maintain the opinion that sound is propagated in the air by means of certain motions or undulations, which the transparence of that fluid prevents our seeing. My experiments with fluids which do not elude the sight, and in which no motion was perceived, notwithstanding the very effectual transmission of sound, may render this in some respect doubtful."

The strength of sounds is greatest in cold and dense air, and least in that which is warm and rarified. "Divers, at the bottom of the sea," says Derham, "can hear noises made above only confusedly: but, on the contrary, those above cannot hear the divers below. Of which an experiment was made that had like to have been mortal; one of the divers blew an horu in his diving bell, at the bottom of the sea, the sound whereof, in that compressed air, was so very loud and irksome, that it stunned the diver, and made him so giddy that he had liked to have dropped out of his bell and been drowned." The sound of a bell under water is much duller and not so loud; and it is a 4th deeper.

Of the Decay of Sound.

" The principal cause of the decay of sound is the want of perfect elasticity in the air; whence it arises that the entire motion of every subsequent particle has not the entire motion of the preceding particle communicated to it, as in the case of equal and perfectly elastic bodies; consequentl the farther the motion is propagated, the more will the velocity, with which the particles move, be diminished: the condensation of air will be diminished also, and the farther the pulse is propagated the more is the density, and consequently the impulse on the drum of the ear diminished."

Of sonorous Cavities, from Dr.
YOUNG.

Mr. de la Grange has demonstrated, that all impressions are reflected by

an obstacle terminating an elastic fluid, with the same velocity with which they arrived at that obstacle. When the walls of a passage, or of an unfurnished room, are smooth, and perfectly parallel, any explosion, or stamping with the foot, communicates an impression on the air, which is reflected from one wall to the other, and from the second again towards the ear, nearly in the same direction with the primitive impulse: this takes place as frequently in a second, as twice the breadth of the passage is contained in 11,300 feet; and the ear receives a perception of sound, thus determined in its pitch by the breadth of the passage. On making the experiment the result will be found accurately to agree with this explanation. The appropriate notes of a room may readily be discovered by singing the scale in it; and they will be found to depend on the proportion of its length or breadth to 11,300 feet. The sound of the stopped diapason is produced in a manner somewhat similar to the note from an explosion in a passage; and that of its reed pipes to the resonance of the voice in a room: the length of the reed in one case determining the sound, in the other, increasing its strength. The frequency of the vibrations does not at all immediately depend on the diameter of the pipe. of reverberated Sounds, from Dr. YOUNG.

"Sound, like light, after it has been reflected from several places, may be collected in one point, as into a focus; and it will be there more audible than in any other part, even than at the place from whence it proceeded. On this principle it is that a whispering gallery is constructed.

"The form of the gallery must be that of a concave hemisphere, as ABC; and if a low sound or whisper be uttered at A, the vibrations expanding themselves every way, will, impinge on the points DDD, and from thence be reflected to E E E, and from thence to the points F and G, till at last they meet in C; where, as we have said before, the sound will be most distinctly heard.

"An echo is a reflection of sound striking against some object, as an image is reflected in a glass. - We have heard of a very extraordinary echo, at a ruined fortress near Lovain,