The Press. — London, England, 1854-07-22 00:00:00

JULY 22, 1854. enveloped in Lady Rycot's cashmere shawl the little fellow on whom he had just conferred twenty thousand a year and a peerage, he called in a peremptory tone to the girl who was assisting Dame Stubton, to "come down, and take care of ' the child.' " All he trusted was that its little fitful life might not hold out till Luke Harston's return. The rain had luckily ceased. And as the doctor splashed his way along the puddley by-road leading to the village, so far from feeling conscious-stricken at the felonious act ho was perpetrating, his sensations, while hugging the little changeling under his warm surtout, were those of a bene factor. He was securing wealth and distinction to the child of poor Bessy ; and her spirit, hovering like a guar dian angel above them, could not fail to prosper his design. By the time he had established his little nursling under the wing of the ignominious nurse who was to afford him the sustenance so much more needful to the convulsed and *agile offspring of the aristocracy, whose hours, nay, whose minutes, were numbered, he began to look upon the new Lord Hilton as almost a creation of his own. The last half of the volume is not so well written as the earlier portion, which raised our expectations. In spite of the defects of construction, " Transmutation," while failing as a novel, may be pronounced readable as a romantic " tale." Sound and its Phenomena. By the Rev. Dr. Brewer, Trinity Hall, Cambridge. London : Longmans. THIS volume is the first of a series of scientific handbooks, which the author proposes to issue chiefly for the use of schools, industrial families, and classes. The nature, transmis sion, and velocity of sound are first described, and then the author treats of various kinds of musical instruments, of the voice, with the apparatus of the larynx, and lastly of the ear, with all that exquisite mechanism which ren ders it one of the most interesting parts of the human frame. Dr. Brewer is successful in showing that all sound is originated by motion, and that it con sists in certain vibrations of the air, which he terms " wave-sounds," buthe appears to imagine that sound is something positive in itself, and does not wholly depend on the construction of the ear. On this point there exists some difference of opinion among those who have studied the subject most closely; and philoso phers have generally shrunk from the conclu sion that sound is nothing more than that impression which is made on the tympanum of the ear by certain vibrations of the external air, which it is expressly formed to receive and to transmit. If such be the correct theory, then, apart from the original impulse given to the air (or other elastic body), there is required, to excite that perception which we call sound, a me dium to convey the original impulse and an ear formed to receive it ; and, if either be wanting, the conditions essential to produce sound are absent. Now, many instances and experiments can be adduced to show that there is no sound without these conditions. Just as certain properties of matter excite the nerves of the nose and produce the sense of smell do vibrations of the air act on the ear and produce the sense of sound. Our organs of sense are all acted on by external influences ; and, strictly speaking, perhaps, the five senses may be reduced to one, that of feeling, as the eye, ear, nose, and tongue act only by directly feeling or perceiving the influences which ex cite them. Throughout his book Dr. Brewer uses the term sound as synonymous with that vibra tion of the air which results in sound when the ear is acted on; and, so far, his language, though sanctioned by custom, is, we think, unphilosophical : Sonnd-waves (he writes) are engendered in the air by whatever gives it a sudden shock : as by the rapid impulses of some vibrating body; by a solid substance rapidly and suddenly changing its place; by the percussion of one stratum of air against another ; or by a combination of some two or more of these collisions. • • • The sound-waves thus created diffuse themselves in concentric circles around the point of their birth, not unlike the ripples made by a stone when it falls into tranquil water. --waves would here, as in all other places igh the book, be a more correct expres than sound-waves, if it be admitted that can be no sound apart from the ear. Brewer then goes on to show how the IeSS of sounds is proportionate to the of the shock- which the air receives : THE PRESS. The analogous ripple on the smooth surface of a lake would be tkr more deeply furrowed by the violent shock of a millstone than if a small pebble were dropped gently into the water. And as the ripple diminishes in force u it recedes, until it is altogether imperceptible, air-waves diminish as they recede from their source until they wholly die away. Ripples in the air, however, are weakened sooner than in water, as they are diffused in all directions, " like the light of a lamp, or a candle ;" and, in accordance with this principle, it is found that sound diminishes in intensity with the squares of its distance from an auditor. Thus : Conceive four men placed at equal distances from each 1 2 3 4 other, as the let ) I t r I ters B, C, 1), E, n 0 n s along the line AE. Let some one tire a pistol at A ; then to C, who is twice a 9 far off as B, the sound will be only one-fourth as loud ; to I), who is thrice as far off, it will be but one ninth as loud; and to E, who is four times the distance, it will be only one-sixteenth. On the other hand, with whatever degree of intensity E may hear the sound, D will hear Rime times as loud, C nine times, and B sixteen times a 9 loud as E. So that the loud ness does not diminish inversely as the distance increases, but inversely to the square of that distance. We do not recollect whether experiment has ever shown that a ripple in the water extends or travels at au uniform rate of speed from its centre ; but this is certainly the case with air or sound-waves.. They progress, whatever their character and degree of intensity, at an equal rate of velocity. That rate in the air is taken for all practical purposes at 1,120 feet in a second, and is found to be in no degree affected by distance from its source. When the air is rarer than common, through heat, sound travels faster than when it is denser than common through cold, the air in the latter ease offering more resistance than in the former to the transmission of the original im pulse it receives. On the other hand, the denser air is found to convey sound more per fectly : As cold condenses the air, sounds are heard more dis tinctly daring a clear frosty day than in the hot noons of summer. For the same reason, they are more audible in the frozen regions than in climates of a higher temperature. Captain Ross tells us, that when he was wintering in the polar seas he could hear the voices of his men in conver sation at the distance of a mile and a half. And Lieutenant Foster on one occasion, during the third polar expedition of Sir Edward Parry, held a conversation with a man on the opposite shore of Port Bowen, the distance between the speakers being smile and a quarter. We have heard Mr. Kennedy (who com manded the Prince Albert in the search for Sir John Franklin) relate that, having once, when alone, lost his way amid the trackless snow, he shouted for help and was answered at a great distance. He followed the sound, and at last came to some Esquimaux. On subse quently comparing the points at which they stood when they first heard each other, he found that they must have been seven or eight miles apart—so far in the dense atmosphere were the air-waves propagated which their voices excited. Though, as we have seen, rare air conveys sound most quickly, yet denser media are stated to propagate sound with far greater velocity than air : Sound propagates itself in water more than four times as fast as it spreads through atmospheric air. * • • • Solid substances for the most part convey sound still more rapidly than water, and in some cases with a velocity 14' or DI fold greater than its rate of motion in atmospheric air. • • • • • •• The rate at which sound is propagated by various solid substances has been carefully tested by Chladin. • • * Glass, iron, and steel transmit sound the fastest. Next, willow, pine, and common deal. Of metals, tin transmits sound the most slowly ; and of woods, oak, walnut, yew, and plam. If these facts are to be taken as literally true, they offer considerable difficulty to the theory, that sound is caused by vibrations per ceived by the ear alone. In the case of water, we am understand that vibrations or pulsa tions made in that fluid may act on the ear in much the same manner as vibrations of air; but it is not so easy to perceive how the ear can be affected through the medium of solid substances, more especially if those substances are not in direct contact with it. Some medium between the original impulse or sound and the ear there must necessarily he, and that medium must plainly be the air in all those cases in which sound is said to be con veyed by solid substances ; but whether the 689 solid body conveys the original impulse from one of its extremities to the other, and then imparts the impulse to the air, or whether the air at the surface of such solid body transmits the impulse much more quickly from the slight resistance of the surrounding atmosphere, deserves inquiry. The following experiments are curious : If. Biot has satisfactorily tested the relative velocities of sound as conducted by air and by metal. A bell was suspended at the mouth of an iron pipe 3,000 feet in length, and a metal ring was so adjusted round the orifice that, when the bell sounded and transmitted its vibrations to the air contained in the tube, the ring struck against the conduit, and communicated vibrations to its metal walls. In this experiment, the vibrations of the ring conveyed along the sides of the tube reached the ear of the observer a con• siderable time before he heard the sound of the bell. The following would be interesting variations of the same experiment, and capable of easy trial. Let some one fire a pistol at one extremity of a long gas-pipe, and the person who applies his ear to the other end w il l hear the report twice. He will hear it almost instanta neously, as it is conducted along the metal walls of the con duit, and again, a considerable time afterwards, as it comes lagging through the ambient air. Or, again : if at early morning, when the air is calm and the neighbourhood quiet, you apply your ear to one end of the handrail of an iron bridge, while some one at the other extremity strikes upon the bar or parapet, you will hear the report of the blow tweet. The first and loudest will be delivered by the metal, and the second by the air. N.B. Sound traverses iron somewhat more than sixteen times hater than it circulates in air. On these facts the reasoning of Dr. Brewer seems to us partly true and partly false : The last two experiments (he writes) could not of them selves be admitted as proof, though they may be taken as corroborative evidence of the point under consideration. It will be seen that the circumstances are not equal, inasmuch as the sound-waves have, in one case, the whole field of air, in which to spread in constantly enlarging con centric circles. whereas in the latter they can propagate themselves only in one direction. In the former case the diffusion is by squares, in the latter by lines. This objection, however, does not rest against the experiment of M. Biot, inasmuch as the air was confined in a tube. And as the result in all three cases is exactly the same, the objection is in reality of no valid force. It appears probable that in the experiment of M. Biot the air in immediate contact with the surface of the pipe might convey the vibrations of the bell more quickly than tho air contained in the hollow of the pipe ; but we do not venture further than to suggest the expediency of more inquiry, with original experiments, on this very interesting subject. If from such a pipe the air was exhausted, and a bell was then rung against its interior side, the experiment would, we imagine, show whether the vibration was really conveyed by the metal or by the air in contact with it. That solid substances are not of themselves, apart from the air in contact with them, adapted to the transmission of those impulses which produce sound, appears from the fact that sound is not conveyed through them when they are of any considerable thickness. A stone wall, a thousand feet in length, would convey a whisper along the whole extent of its surface, but. a much louder sound would not be conveyed through a stone wall of a single foot in thickness,—a strong presumption that it is really the air in contact with solid sub stances which conveys the impulse resulting in sound, and not the solid substances them selves. That sound does not exist apart from some media for its conveyance, and apart from the ear communicating with such media, is proved by numberless and familiar examples. If a bell be rung in the exhausted receiver of an air-pump, no sound is apparent ; admit the air by degrees, and by degrees the sound is heard. Place over the receiver a larger re ceiver, and exhaust the air from the second while it is retained under the first, and the ring of the bell will again not he heard, be cause the communication of air between the bell and the ear is cut off. Supposing a per son were placed under the first receiver, be would hear the ring plainly enough, while to a person outside of the second receiver the clapper would seem to strike the bell without causing any sound whatever. The conclusion seems to be, that sound consists alone in the adaptation of the ear to receive, and to per ceive, vibrations of the air. Some paragraphs here on the effects per ceptible by persons who have ascended to a highly-rarefied atmosphere point to the same conclusion : Air- , throuo Sion ti there Dr. B loudno force 4