| Art. XX. Memoirs of the Literary and Philosophical Society
of Manchester. Vol V. Part II. Cadell & Davies. London. 1802.
An Investigation of the Method whereby Men judge, by the Ear, of the Position of Sonorous Bodies, relative to their own Persons. By Mr. John Gough. This paper aims at explaining a very curious set of phenomena which have seldom been discussed by philosophical writers. The investigation displays some ingenuity and original argument, though we are afraid that the solution still remains hypothetical and loaded with all its former difficulties. The author distributes his subject into three distinct considerations - First, He attempts to explain the mode by which men ascertain that sounds proceed from some point directly before or behind their heads, which he denominates `direct hearing:' 2dly, The mode of determining that sounds proceed from one side or the other, which he denominates `oblique hearing:' And, 3dly, The mode of ascertaining that sounds proceed from above or below. With regard to the first of these (`direct hearing'), our author illustrates the common notions upon that subject, by the following apposite plan. He supposes an imaginary right line drawn across the head, joining the two ears, and another line passing from the front to the back of the head, bisecting the former at right angles, If, then, a circle be described upon the first line as a diameter, this circle may be said to represent the head. A sonorous body, then, situated anywhere in the straight line produced, bisecting this diameter at right angles, will be equally distant from both of the extremities of this diameter, viz. the ears. The vibrations or pulses of sound proceeding from it, will therefore fall with equal force upon both ears; and hence, our author declares, the situation of the sonorous body is determined by the person to be either directly before or behind his head. This he considers is the case of direct hearing. Again, upon the supposition, which is very universally admitted, that the undulations or vibrations occasioning the sensation of sound, move in a straight and uniform direction from the sonorous body, any solid interposing obstacle must shelter the parts situated immediately on the opposite side of it, from the direct reception of these vibrations: so that, if the sonorous body be placed any where out of the right line just mentioned; or, in other terms, if it be placed So, that a straight line drawn from it to the point of bisection in the line passing across the head and joining both ears, shall form an angle which is not a right angle, a part of the head must intercept vibrations, and prevent them from arriving directly or with their full force, on that ear which is thus sheltered. This is obviously demonstrated, by drawing from the given point in which the sounding body is placed, two lines which shall be tangents to the circle before mentioned: then will these lines exhibit the direction in which the vibrations proceed, and shew, that while they fall immediately upon one ear, they are interrupted in their progress to the other by a projecting part of the circle or supposed head. Thus far we perfectly agree with the ingenious author: indeed we conceive this to be little more than a mathematical illustration of a very common notion, that experience teaches us to refer the situation of sonorous bodies to the right or the left of us, according as the ear of one of these sides receives a stronger or more immediate impression than that of the other. The author informs us, that he himself is peculiarly sensible of the slightest obliquity compared with the plane of the horizon) in the direction from whence sounds proceed. This, however, is not a very common faculty - the result, perhaps, in the author's case, of a peculiarly sensible organ, and frequent attention to the process of hearing. Our author next attempts to `investigate the perception which, determines the place of a sounding body to be in front of the hearer or behind him.' We shall quote his reasonings at length in order that their full force may be comprehended by our readers. The head is a sensitive solid, and it perceives the impulses made on it by sounds much more exquisitely than men generally imagine. This sensibility is strongest in the auditory passages, and, next to them, on the parts immediately adjacent to the ears; nevertheless, it diffuses itself more or less perfectly over the face, forehead, and temples, as well as all the external teguments of the skull. The sensation in question being of but little use independent of its connexion with hearing, we for the most part mistake its true situation, and refer it to the organs of this sense, unless some circumstance, resembling the succeeding experiment, should happen to discover the nature of it to us. If any one will take the pains to close the orifices of his ears with wet paper, and will hold two slender rods of wood to his forehead, or to one of his temples, taking care to keep the ends which are in contact with the skin separated by a small interval: and let another person at the same time touch the opposite ends of the rods with two watches, one of which does not move: the beats of the active watch will immediately pass along the stick, and make a sensible impression on the spot where its other extremity rests; which proves, that the bones of the head do not simply conduct sounds to the auditory nerves, but that the external teguments of this member also assist in discovering the directions of sounds by their sensibility. The same apparatus may be used to shew, that all parts of the head are not equally alive to the impulses of sounds; for a stick which is of a proper length to impress the beats of a watch very faintly on the ear and parts adjacent, will prove too long to produce the same effect on the forehead, which is nevertheless much more exquisite in its feelings than the back part of the head. pp. 638-39.It is difficult to comprehend what power or faculty our author here means to ascribe to the bones and integuments of the skull. There are only two, relating to the present subject, of which can form any distinct conception. Either they possess a sentient and auricular faculty, or they act merely as conductors of vibrations. Now, upon the former of these propositions only can the author's reasoning rest. And that it is totally untenable, in other words that the bones of the skull and its integuments do not possess in the slightest degree an auricular faculty, is demonstrable from this fact, that in cases where the ears are effectually stopped, or in persons who are deprived of these organs, no sensation of sound can be produced, however loud that sound be, or however closely the sonorous body be applied to the integuments, provided only it do not touch: but on the other hand, the instant that the sonorous vibrating body comes into contact with the head, the perception of sound is immediate and distinct. Whence we infer, that the bones and integuments of the head act merely as conductors of the sound or vibrations to the organs of hearing. It is true, that a sensation is produced in the head, at the point of contact; but this is merely a matter of feeling, and perfectly distinct from the other sense. That the situation of sonorous bodies, therefore, is determined by the hearer to be before or behind him, by means of the different qualities with which the front and back part of his head are endued, we confider not only as hypothetical, but palpably untrue. But the extension of this hypothesis, by our author, to the mode by which we determine whether sounds proceed from a point above or below us, we conceive to be even more fanciful than the former. This `difference,' therefore, `between the front and back part of the head;' and again, `the want of sensibility in the upper part of the head and the lower part of the face' we must reject as entirely unfounded in fact or probability. From this subject, our author proceeds to investigate the nature of ventriloquism, a curious, and, as yet, unexplained subject. And here again we are disposed to differ very materially from his opinions. `He who is master of this art,' says he, `has nothing to do but to place his mouth obliquely to the company; and to dart his words, if I may use the expression, against an opposing object, whence they will be reflected immediately, so as to strike the ears of the audience from an unexpected quarter, in consequence of which the reflector will appear to be the speaker.' p. 649.Though this comprehends the scope of the author's doctrine, we are of opinion that it affords a deficient and inadequate explanation even of the case that he relates, in which the ventriloquist performed his operations in a confined room. The power of projecting the voice against a plain wall, so that it shall be reflected to a given point, is difficult, and we may almost say impossible of attainment. But~ granting that this power were attained, the reflected tones of the voice must be a mere echo, whilst the sounds proceeding immediately from the mouth of the speaker being both louder in degree, and prior in point of time, must necessarily, as is the case in every echo, drown the first parts of the reflected sounds, and make the remainder appear evidently different from the original. The author seems to have been led into this theory by the analogy of light, without perhaps duly considering that the particles of light move successively in direct lines; whereas the undulations of sound must necessarily expand and enlarge, as they proceed on from the sounding body. But the feats of ventriloquism are often performed sub dio, when no means for reflecting the voice can be present, and where, of course, the author's doctrine cannot in any respect apply. He has omitted to mention a cause which has a very powerful influence in effecting the deception, viz. the expectation excited in the spectator or hearer, by the artist having previously informed him from whence he proposes to make the sounds proceed. This circumstance of raising expectation almost to belief, aided by a peculiarly happy talent for imitating singular or striking sounds, such, for example, as the cries of a child in the act of suffocation, is perhaps a more probable explanation of the phenomena of ventriloquism. As an appendix to this paper, the author has added a short disquisition on the theory of compound sounds, in which he endeavours to maintain, that Dr Smith's hypothesis on this subject has not been in the least invalidated by a late theory of Dr Young. Our author agrees with Dr Smith in opinion, that `a number of simple sounds may exist in concert, and strike the ear in a distinct manner, without suffering any interruption in their motions from the interference of their pulses.' He adduces many acute arguments, and mathematical demonstrations, to prove `that there are as many sets of pulses in an aggregate of sounds, as that aggregate contains elements, and that the coalescence of two sounds is impossible.' Now, we conceive the prominent defect of our author's hypothesis to be, his confusion of the abstract mechanical nature of sounds, with their sensible effects upon the human ear. We agree perfectly with him, that in a band of music, every separate instrument, or cause of peculiar vibrations must produce separate and peculiar pulses upon the air; at the same time, however, that the ear may not be able to detect the appropriate and distinct sounds of each. It is indeed a mathematical absurdity to talk of the absolute coalescence of two sets of pulses, as they must necessarily proceed from different points, and the direction in which they flow must of consequence be in some degree varied. It is nevertheless an obvious and well ascertained fact, that in a concert of musical instruments, the ear only occasionally distinguishes the separate causes or sources of vibratory sounds. This unison, indeed, which deceives the hearer, forms what is properly termed harmony. There is one view of this subject which may perhaps illustrate the distinction that we wish to establish between the absolute and mathematical nature of sounds, or, to speak more philosophically, the causes of sounds, and their sensible properties on the ear. A correct and harmonious concert of musical instruments may produce sets of vibrations or pulses, which have a uniform tendency to coalesce, but which may nevertheless proceed on indefinitely, approaching nearer to each other, without ever constituting an uniform compound. In the same manner, a hearer may place himself so near to a band of musical instruments, as to be enabled to distinguish the separate sounds proceeding from each; but in proportion as he recedes, their united sounds become more blended and harmonious, until he comes first to lose some of the feebler sounds, and at last to have no effect at all produced upon his ear. But the author attempts to demonstrate, by a mathematical process, what no mathematical reasoning can prove, viz. `that a number of distinct cotemporary sounds cannot do otherwise than produce distinct sensations.' If, by distinct sensations, he means sensations distinctly felt by the individual, the fact overturns all these deductions. But if, by this expression, we are to understand distinct causes, or indefinitely small and separately imperceptible parts of that whole which constitutes one distinguishable sensation, then we shall be ready to admit that this is at least a highly probable, and very philosophical conjecture. Some men hear more acutely than others, and some animals perhaps more acutely than men. It is impossible, therefore, to bring matters of bodily sensation to the test of mathematical argument or the correctness of mathematical precision. Unsigned article in Edinburgh Review, or Critical Journal, 2 (1803): 192-6. |
Compiled by Steven Connor.
as part of The
Dumbstruck Archive, a continuing, online supplement to Dumbstruck:
A Cultural History of Ventriloquism (Oxford: Oxford University Press,
2000).