ADDENDA TO CHAPTER VI. EVOLUTION OF SOUND ASSAILED. This work on sound has been published more than two years, and no attempt at reply has been made, with the single exception of the following Review by Prof. R. L. Brockett, A. M., Professor of Physical Science in Western Maryland College. The criticisms of this scientist were called out at the request of Rev. Dr. L. W. Bates, of Lynchburg, Va., who sent a copy of the work to him requesting his examination and opinion. The following extracts from that opinion were sent to us by Dr. Bates, and at our request the author wrote a reply, all of which are given herewith. In connection with this review and rejoinder, we take the liberty to print also the critical observations of a very careful investigator, Prof. L. L. Kephart, A. M., for five years Professor of Physical Science in Western College, at Western, Iowa, with the author's answers and the Professor's final acquiescence, which, it is believed, will throw some light on the subjects discussed in Evolution of Sound. It is readily comprehensible that even an able scientific investigator, like Prof. Brockett, might be mistakenly led to reject such a radical departure, opposing, as it does, a theory of science never before called in question, and one which his long habit of teaching had made almost a part of himself. But it is insupposable that an equally competent critic, and with equal experience, facilities and prejudices, like Prof. Kephart, for example, after studying the treatise for months, should mistakenly give it his unqualified indorsement. This distinction in the weight of testimony, between the rejection and approval of a new hypothesis in science, would seem to be self-evident. Among the many professors of physics, whose testimony is unequivocal in favor of the new hypothesis, we take the liberty of naming Professor L. M. Osborn, LLD., Professor of the Physical Sciences in Madison University, at Hamilton, N. Y., who closes a recent letter to us in the following words: "The part on sound I prize very highly-a new departure that must be permanent, and lead to many modifications of old notions. L. M. OSBORN." Such decisions as this are not negative, but positive. Hence they carry with them the weight of unquestionable reliability. We will only add that, although this treatise has been for nearly two years in the hands of the three eminent authorities on sound (Tyndall, Helmholtz and Mayer) reviewed by the author, yet no attempt at reply on their part has thus far been made. This silence cannot be construed to imply that the arguments are regarded by them as too trivial to be considered worthy of notice, particularly in view of their unconditional approval by so many college professors whose ability to judge correctly upon this subject surely entitles them to some respect. It can only imply, in the opinion of one professor who has abandoned the wave-theory of sound, that these authorities on acoustics, realizing the unpleasant predicament of accepting the new hypothesis and thereby admitting their own exhaustive treatises on the subject without foundation, have adopted the policy of silence, hoping that by ignoring the whole matter as if it had no existence, the author's obscurity would allow the work to fall still-born, and in this manner prevent a sensation in the scientific world, such as the total destruction of a universally-accepted theory must necessarily produce. Whether or not this view of the animus of these eminent scientists is correct, it will not be an easy matter to convince thoughtful investigators that such a revolutionary departure in science, as this monograph, is unworthy of reply, especially arguments which can command the approval of experienced professional acousticians. We ask students of science to read and weigh these arguments, and then judge for themselves if the wave-theory of sound has not seen its day? PUBLISHERS. Professor Brockett's Review. "I have carefully read it [Evolution of Sound], -given it much and close examination,-and my conclusions are that the book, as an argument against the undulatory theory of sound, is an utter failure. It is ingeniously written, is certainly the work of a man who has a thorough knowledge of the subject, but who covers up his weak points with a great flow of language, and makes so many bold utterances about overwhelming his opponents, that readers who are not au fait in the science of acoustics are apt to be misled. His hypothesis of corpuscular emissions is exceedingly defective, and requires so many modifications to meet particular cases, that it needs only to be stated to enable one to find insurmountable objections. 'Wilford' himself admits that there are difficulties, but consoles himself that it is the only refuge, the current theory being overthrown. 44 The greatest objection I have to the book is, that the author uses the accurate knowledge he possesses, (for what reason I can not tell) to teach This is a charge no one should make without proof. Let me produce it. In the first part error. of the Review,' where he labors to show that the pulsations of a sonorous body do not and can not disturb the air as acousticians claim, and illustrates by showing that he could not, in a closed room, with a fan, cause a gas light to flare twenty-five feet off, under five seconds of time, and with all the effort of one-man power'; and, in a triumphant way, asks how the prong of a tuning-fork could throw off air-waves, when it only moves eight inches a second, and set in motion another tuning-fork 180 feet off tuned synchronously, while his fan moved over an arc of seven feet and could not cause air-waves to be felt only twenty-five feet [away], and then only after a lapse of at least ive seconds. "Now there is no analogy whatever between the motion of a tuning-fork and that of the fan, and he must have known it. The fan moves seven feet and the fork eight inches, he says, in a second; and his argument is that as the air, by its mobility, moved around and closed up so easily after the fan as not to disturb the rest of the air, that it is impossible to believe that the tuning-fork, that moves only eight inches in a second, could disturb the air at all. Let us consider this. All air-waves are not sound-waves. When we wave our hand, or move a fan, or in any other way move the air, we produce air disturbances or waves; but sound waves are only produced by the motion of elastic bodies giving instantaneous pulses. It is true that the prong of the fork moves only eight inches in the aggregate, in a second; but in that time it makes 384 pulses, every one of which produces a sound wave. His fan, with the one-man power,' can only disturb the air, and can not produce a sound-wave, because it (the fan) is not elastic; and, if it were, even his one-man power,' without the aid of machinery, would not be able to give the requisite velocity to produce a sound-wave. His fan makes one vibration or pulse while the fork-prongs make 384; the one disturbs the air by moving slowly through it, which disturbances are easily adjusted by the mobility of the particles; while the other, by its instanlaneous pulses, sets in motion sound-waves, that pass from the elastic body as a centre outwards in all directions. Hence his sneer at acousticians ་ when they say the prongs of the fork advance rapidly; and he tells us that this rapid advance is only eight inches in a second, falls short of the mark. Is not 384 pulses or vibrations rapid motion?-and is not one pulse of seven feet per second slow motion in comparison? If Wilford wished to state the case fairly, he would not have put it as he has. He knew better. * * * * If every move. ment of the air produced a sound-wave, we would live in a bedlam, and your congregation would not be able to hear you preach while the ladies were using their fans; nor does this motion of the fans interfere with the sound-waves from your voice, and their rapid motion is but slightly affected ever by a strong wind. 44 Wilford does not seek to tell us what a sound, wave is. He makes extracts from acousticians, and calls on his readers to observe that he is very fair; but, if you will examine the quotations, you will see that his purpose is to pick out a sentence here and there, and interpolate occasionally some qualifying remark; **** not to present the matter fairly, but to overthrow the current theory at whatever expense. * * * * "A sound-wave is produced by an instantaneous vibration or pulse of an elastic body, as a musicbox, when playing under a receiver and pump out the air, the music will cease, or rather we will not hear it, but will be heard again when the air is let in. In like manner, by observation, we know that the air-wave is a sphere—like a soap-bubble,—because we hear the sound in every direction from the sonorous body. Having, then, these two points as data, and connect with them the known fact that only instantaneous pulses will compress the air suddenly and constitute a sound-wave, we find, then, that at every pulse of an elastic body a spherical globe of air is made at the body, that vibrates to and fro, but does not advance; but, owing to the structure and properties of the air, not neces sary to enumerate here, this sound-wave sets in motion-forms-another sound-wave, and it another, and so on, sometimes to the distance of many miles. When, then, we hear the sound of a bell miles away, or the whistle of a locomotive, it is not the sound-wave, that was made at the place where the bell or the locomotive is, but it is the soundwave made of the air where the listener is. ** It is not the air that has traveled over the intervening space that strikes the tympanum of the listener, but the air around the listener that has been set in motion hy the advance of the series of sound-waves, which stops only when their force has been expended. This rapid advance of the form of the wave is the reason that winds affect so little their progress; besides, elastic fluids, as air and gases, pass in currents through each other without creating but little disturbance. "Now, any one can see that if these waves are made as claimed, the air all around the circumfer ence of the sphere must be compressed, and the air of the interior must be rarefied. Sudden compression of the air causes heat, and rarefaction causes low temperature. This I can show you with a piece of apparatus belonging to the college, by means of which I can compress the air, and ignite tinder, causing it to burn freely; and yet Wilford has the hardihood to use ridiculous phrases in alluding to these condensations and rarefactions, as if they had no existence in fact. "All of our experience goes to show that the distance sound travels, and the distinctness with which we hear it, depends entirely upon the condition of the air. The more homogeneous the air is, the better medium is offered to the progress of the sound-wave. As we ascend through the air, the sound grows feebler; and at the tops of very high mountains, pistol-shots are no louder than pop-guns make at the base. But, besides all this, and a plenty more that might be written. the undulatory theory of sound is established mathematically. All the phenomena of sound have been examined in connection with the current theory and mathematical formulas have been applied in the most rigid manner; and, in every instance (sometimes correcting error, however), the theory has proved sufficiently able to meet every case. His cheapest game would have been to apply his hypothesis to the phenomena of light, because it will give, in some instances, a plausible explanation; though many of the phenomena-notably that of refraction-it does not and can not explain; and even Sir Isaac Newton, the originator of the corpuscular theory of light, admitted his theory did not satisfactorily account for the phenomena. *** "I find Dr. Drinkhouse [editor of the Methodist Protestant, Baltimore, Md.] has commented favorably upon the part entitled The Problem of Human Life. I do not know anything about that part of the book; but if he expects any help in his Problem, by showing that sound is made of corpuscles of matter, I fear his solution of the Problem is not a correct one Dear Sir: Your letter to Hall & Co., inclosing copious and verbatim extracts from Prof. Brockett's review of Evolution of Sound, was handed to me for my examination and reply. Allow me to thank you for the interest you have taken in securing so competent a scientist to review the work, and one, too, who has proved himself not afraid to risk his reputation as a physicist and acoustician on the venture he has made; and I here place it to his credit that he is the first scientific investigator who has shown a willingness to attack these arguments against the current sound-theory, though the monograph has been in the hands of hundreds of professors of physical science and scientific journalists for months. I must say, however, in all frankness, that I am surprised, no less than gratified, to know that this is the best that can be done in favor of the wavetheory, and the worst than can be said against Evolution of Sound, by a skillful professor of physics. That he has done his best to convince you that the book, as an argument against the undulatory theory of sound, is an utter failure," there can be no doubt; and the very fact that he has "carefully read it,-given it much and close examination," is conclusive on its face that had there been weaker or more vulnerable points to assail, he would have selected them in preference to the line of argument chosen. Hence, in meeting this assault, I shall feel that I am not wasting my time on matters of trivial importance. But first, let me say, I forgive the Professor for his personal and unkind thrusts, virtually charging the author, though admitting his "thorough knowledge of the subject," with positive dishonesty in using "the accurate knowledge he possesses * * * to teach error," and who" covers up his weak points with a great flow of language," in order to mislead the readers of his book, who are not au fait in the science of acoustics," even accusing him with misrepresenting the authorities he quotes by a purpose to "pick out a sentence here and there, and interpolate occasionally some qualifying remark: ***not to present the matter fairly," etc. Although I forgive, I will not forget; and will only say here that I defy any man to place his finger on a single quotation in the hundreds made in The Problem of Human Life, including Evolution of Sound, which does not fairly represent the meaning of the author cited. An educated man ought to know that explanatory interpolations, thrown into a passage quoted, are entirely allowable, to save quoting the context or to avoid much longer explanations afterward, provided such interpolated remarks are duly bracketed. But enough of this. I now come to the subject-matter of the review, and I am only stating what you, no doubt, Lave already observed, when I say that the entire argument is devoted to a single phase of the scundquestion; and, though variously elaborated, involves but one assumed principle or law of science, namely, that there are two kinds of air-waves, differing from each other in the most essential characteristics,-one kind, such as those produced by a fan, traveling only about five feet in a second and only capable of reaching to a distance of twenty-five or thirty feet in a still room; and another kind, called "sound waves," produced by the motions of a tuning-fork's prong or other vibrating sonorous body; and of such an entirely different nature that they are capable of making headway through the atmosphere at a velocity of 1120 feet a second, and to a distance, often, of many miles. The reason for Professor Brockett's selecting this phase of the discussion, and devoting his entire review to it, is apparent. This law of two kinds of air-waves, with the essentially different charac teristics just pointed out, lies at the very foundation of the wave-theory of sound, and without which it would have no existence, as every tyro in science knows; and this law being seriously assailed in Evolution of Sound, he saw that unless it was rescued from the attack, the whole undulatory hypothesis must fall to the ground. Hence, he chose to direct all his force to this single aspect of the question. I make no objection to the way he states my argument based on the fan experiment; and I only wish to impress the fact upon your mind that he admits, as he is necessarily obliged to do, the result of that experiment as I have given it, namely, that the waves thus produced travel only at a very slow speed, say about five feet in a second, and to a distance of only about twenty-five or thirty feet in a still room; while he attempts to account for it by saying: His fan makes one vibration or pulse while the fork-prongs make 384; the one disturbs the air by moving slowly through it, which disturbances are easily adjusted by the mobility of the particles, while the other, by its instantaneous pulses, sets in motion sound-waves." As he has thus admitted the correctness of my explanation of the fan experiment, I now propose to show that it is the fatal though unavoidable admission of his review, and that by it alone he has annihilated the wave-theory of sound, as well as his entire argument, for, by this admitted fact of the fan sending off air-waves at a very low velocity, it will be conclusively proved that the so-called "instantaneous pulses," or motions of the tuningfork's prong, to which he so repeatedly calls your attention, can not by any possibility send off airwaves any swifter in proportion to their own rate of velocity than can the motions of the fan. He has selected the battle-field after "much and close examination," and upon it shall the battle be fought. My first appeal shall be to logic and reason, without any special reference to this review, but only as relates to the improbability of the existence in Nature of any such essentially different varieties of air-waves as the theory requires; after which I will give the positive proof, in various ways, that such different varieties of air-waves can have no existence in fact. It is well known to every student of physical science that sound travels through all solid and liquid bodies with even greater volocity than through air. Professor Tyndall says: The velocity of sound in water is more than four times its velocity in air. The velocity of sound in iron is seventeen times its velocity in air. velocity of sound along the fiber of pine wood is ten times its velocity in air."-Lectures on Sound, P. 47. 99 66 Let us now see how this law of two different kinds of air-waves, upon which the very life of the wave-theory depends, will behave, when we try to harmonize it with the propagation of sound through water and iron. Bat before testing it thus, I wish barely to call your attention to this most suggestive fact, that in all the published works on sound not one single writer has ventured to discuss the nature of this indispensable wave-motion in water, iron, and other solid and liquid bodies. They cautiously steer entirely clear of these ugly questions of "condensations," "rarefactions,' wave-lengths," oscillations to and fro" of the wave particles, and “superpositions" of a number of systems of waves at one time passing through iron, although they talk and write learnedly and confidently enough of all these things taking place in the passage of sound through air. Why this apparently studied silence in relation to sound-waves in water and iron, when these writers know very well and admit that sound travels with greater facility and with many times greater velocity through them than through air? I will tell you the reason, whether they think of it or not. Air is invisible; and it becomes entirely convenient to fabricate and formulate all this scientific nonsense about atmospheric "condensations," "rarefactions," "oscillation of the particles to and fro,' superpositions," etc., as the absurdity of the thing can not be detected, since the atmosphere can not be seen. But should they attempt to apply their philosophy of amplitude, or "to and fro" motions of the particles to iron, or even water, where the particles are visible under the microscope, they must know, if they reflect at all, that the shallow deception would be exploded, and that all this pretended wave-motion as the principle of soundpropagation would be at once demonstrated to have no existence in fact. But as long as they can keep us away from iron, or anything we can examine with the microscope while sound is passing through it, and confine our attention to a substance like the air that can not be seen, there is no end to theit rhetoric about this "spherical globe of air" "like a soap-bubble," as Professor Brockett expresses it, which forms in a circle all around the tuning-fork! What a pity that some one of his students should not request him to give an ocular demonstration of his theory of air-waves Ly generating a "spherical globe" of iron or water like a soap-bubble," and let them look at it under the microscope! These bubbles ought surely to form in water and iren, if they do in air! But there is not the least danger that advocates of the wave-theory of sound will ever perpetrate such a folly as even to allude to these little globes and spheres caused by sound in connection with any substance that can be seen, knowing, as they must, that such a legitimate application of their philosophy to visible Lodies would instantly explode the "scap-bubble" fraud, and turn the whole wave-theory into ridicule! But now let us try to test the truth of this theory in air, by applying it to water. First, then, I state the logical and incontrovertible principle, which no one will question, that if air-waves constitute sound-waves in air, then water-waves constitute sound-waves in water, and iron-waves constitute sound-waves in iron. One has no need of a scientific education to comprehend cr see the force of this logical truism. Then, as sound-wares in water must be water-waves, just as sound-waves in air must be air-waves, it involves the unavoidable necessity of two kinds of water-waves, the same as Prof. Brockett's two kinds of air-waves,- one kind slow (from two to thirty feet a second), and the other kind fast (4,500 feet a second),- one kind zissible and the other kind invisible, even under the most powerful_microscope,—one kind with an amplitude or depth of furrow equal always to one foot for every ten feet of wave-length, while the other kind is devoid of all amplitude, not even enough to be observed under the microscope, since to motion of the water-particles to and fro" takes place by the passage of sound, and hence there are no waves, because such a thing as a system of waves without amplitude is as absurd as to talk of a rainbow without a curve. But here the wave-theory of sound runs against an inexplicable difficulty, and one that hopelessly crushes it. In Evolution of Sound, at page 318, and elsewhere, I quote from the highest living authorities numerous passages declaring that soundwaves are essentially identical" with water-waves, are precisely similar" to them, and travel “exactly in the same way." These are the very words of an authority no less than Professor Helmholtz himself, the greatest living exponent of the wavetheory of sound. But, mark you, he said this with reference to atmospheric sound-waves, the thought never entering his mind at that instant, that sound passes through water with much greater facility than through air, and consequently should have much more distinctly marked waves! Had this idea flashed across his mind that sound passes through water, and that, too, in the form of waves,-he would instantly have seen the ridiculous plight in which he had, unwittingly, involved the entire wavetheory; for if sound-waves in air are essentially identical" with water-waves, and if they are “pre cisely similar" to them, and if they travel "exactly in the same way," then sound-waves in water must also be precisely similar" to water-waves, must be "essentially identical" with them, and must travel "exactly in the same way;" and hence it follows, monstrously absurd as it is, that sound-waves in water are nothing more nor less than water-waves! This is inevitable, if there is any meaning in words. And thus we not only annihilate the wave-theory of sound both in air and water, but we upset all science in regard to the velocity of sound in different substances. Observation assures us that all Sounds travel through water at the uniform velocity of about 4,500 feet a second, whether such sounds are of the highest pitch, having a theoretic wavelength of only one foot, or are the low notes of the piano, with theoretic wave lengths in water of over one hundred feet. But here comes Prof. Helmholtz, who authoritatively denies this feature of science, and declares that sound-waves travel "exactly in the same way as water-waves! What, then, is the result? Why, simply that all observation in regard to the velocity of sound, whether in air or in water, is wrong from beginning to end; for, as sound-waves travel "exactly in the same way as water-waves, there ought to be no uniformity at all in the velocity of sounds of different pitch, and consequently of different theoretic wave-lengths, because it is overwhelmingly established in Evolution of Sound, for the first time in any scientific work, that the velocity of all waterwaves must vary, by the necessity of wave-motion, in exact proportion to the wave-lengths of any given system, the small waves of one inch wavelength, caused by the falling of drops of water, traveling only two feet in a second; those caused by a passing steamboat, with ten feet wave-length, traveling seven feet in a second; while ocean billows, with thirty to one hundred feet wave-lengths, travel from fifteen to thirty feet a second. (See pages 317 to 326.) This single consideration, therefore, without the aid of another proof, overthrows the wave-theory of sound in air as well as in water, because in the only wave-motion we can see and measure, we find that an immutable law prevails, namely, that the velocity of all waves is variable and in proportion to wave-length, while sounds, whether high or low in pitch, have but one uniform velocity in any one substance, thus demonstrating that sound does not travel by wave-motion at all. I will here venture the assertion that Professor Brockett never read this argument at all, notwithstanding his much and close examination;" for, if he had, he would have been totally confounded by the fact that the very nature of wave-motion flatly contradicts the wave-theory of sound. But I have not yet reached the culmination of these logical and common-sense reasons for rejecting air-waves as the principle of sonorous propagation, nor have I touched upon the greatest absurdities which such an assumption necessarily involves. I have already stated the logical fact, that, if soundwaves in air constitute air-waves, as Prof. Brockett teaches, and as admitted by all writers on the subject, then sound-waves in iron constitute iron-waves. It is impossible to evade this. Further, as atmospheric sound-waves are formed by "a small excursion to and fro" of the air-particles, thus constituting their "amplitude," without which air-waves could not exist (see many quotations to this effect, Evolu | tion of Sound, p. 78), it follows that iron soundwaves must also be formed by "a small excursion to and fro" of the iron particles, thus constituting the necessary" amplitude" of iron-waves, and without which a wave" is a nonentity! But as no suci. excursion to and fro" of the iron particles occurs in a solid mass of iron when conducting sound, even when examined under the most powerful lenses, and consequently no amplitude "exists in such supposed iron undulations, it demonstrates that there is no wave-motion in iron as the result of sound, and hence that sound must pass through iron by some other law; and if through iron then through air, as there evidently, can be no two different modes or principles of sound-propagation through different substances,-one wave-motion, and another something else! Hence, the undulatory theory of sound, even in air, breaks down of its own inherent weakness. Should it be said, here, that in the propagation of sound through iron the particles may move "to and fro," producing the necessary amplitude" as required in all wave-motion, but not sufficiently to be visible under a microscope, then I answer that such invisible and infinitesimal motion, even if it occurs, would not constitute sound capable of addressing the human ear, because the eye is admittedly one of the most refined and sensitive of the avenues to perception; and this being so, these supposed motions of the iron particles, which can be so easily heard by the unassisted ear, should, if they take place at all, be plainly visible to the naked eye! But as this assumed "amplitude" or motion of the particles can not be seen when the sight is magnified a million fold, it is conclusive evidence, on its face, that such motion, if it takes place at all, is a million times too trifling to be heard! Thus, again, does wave-motion in iron break down; and with it, as a necessary corollary, wave-motion in air. Let Prof. Brockett try his hand on this problem, instead of skipping "here and there" and dealing in glittering generalities. But it is maintained by Professors Tyndall, Mayer, Spice, and in fact all writers and lecturers on acoustics, that sound-waves can be actually observed to run along an iron bar, if a vibrating sonorous body be held against it. This, however, is only another evidence of a want of thoroughness and critical examination on the part of physical investigators, as will at once appear. There is no question but that a molecular tremor may be dctected running along a bar of iron, when a powerfully vibrating tuning-fork is held against it, be cause this tremor can be felt at a distance of many feet from the fork. But, strange as it may seem, these tremors which are but incidental to the fork's vibration, having nothing whatever to do with the accompanying sound-pulses, are mistaken by physicists for the sound itself, though it is easily demenstrable that such tremor does not travel along the bar at a velocity of one hundred feet in a second, while it is well known that sound itself passes through iron at a velocity of more than 19,000 feet in the same time, or more than twenty-five times swifter' than a rifle-bullet. To demonstrate the truth of this distinction, an acoustician needs only to place his ear and hand against one end of a long strip of pine wood, whilst his assistant draws a saw, or other rough instrument, across the other end, and he will find that each movement of the saw will be heard very distinctly some time before the incidental tremor will |