tion my objection as well. Should the experimental test decide against me, I will willingly retract my calculations, the more so because they are only approximately correct. This may be brought about either by the new experiments of Messrs. Stewart and Tait, or by Sir William Thomson's promised determination of the radiation of heat in absolute measure. But so long as this experimental test is wanting it would be idle to continue a dispute about an unproved hypothesis. Breslau, February 13, 1869. XXXIX. On the Falsetto or Head- Sounds of the Human Voice. By WILLIAM MARCET, M.D., F.R.S., Assistant Physician to the Hospital for Consumption and Diseases of the Chest, Brompton*. THE HE consideration of the cause of the head-notes of the human voice is of much interest, not only in a physiological point of view, with the object of accounting for the production of those wonderfully soft and penetrating sounds in which Swiss and Tyrolese singers are so remarkably proficient, but also for the purpose of explaining certain morbid changes of the human voice not unfrequently met with. Let me premise that, by means of the laryngoscope (a small mirror so constructed as to allow the observer to view the inside of the larynx and the action of its various parts in the production of sound), the phenomenon of phonation can be investigated with great minuteness. There are, moreover, certain changes of form the larynx undergoes in the act of phonation, and bearing on the subject of the present communication, which can be determined by external observation, much in the same way as we can ascertain by looking and feeling, that the windpipe is raised in the act of swallowing. The vocal apparatus consists of two folds of the mucous membrane of the larynx, supplied at their free edge with bands of elastic tissue. These folds are opposite each other in a horizontal plane, and in the antero-posterior axis of the larynx. Their lips or free edges may be brought so close as to touch one another, while at the same time they may be subjected to a certain degree of tension; if under these circumstances air be blown out from the lungs, these laryngeal folds or vocal cords will be made to vibrate, emitting a sound. It is considered by J. Müller and others that the human chestsounds are owing to the whole breadth of the laryngeal membranes entering into vibration, while the head-sounds are due to the vibrations being confined to the margins or mere edges of the membranes. Helmholtz thinks the head-sounds are caused * Communicated by the Author. Phil. Mag. S. 4. Vol. 37. No. 249. April 1869. U by the removal of the mucus which constantly moistens the rim of the cords; their edges thus become sharper and their weight less, while, their elasticity remaining the same, they are shaken into more rapid tremors* The observations I have had the opportunity of making appear to show that the head- or falsetto sounds are really caused by the vibrations being confined to the rim of the cords; and I have been able to determine with the laryngoscope the conditions of the larynx which give rise to these sounds. When the larynx is examined with the laryngoscope during the act of phonation, the vocal cords are seen to approach each other throughout their whole length and parallel with each other, till they appear in contact, or very nearly so. Any circumstance which interferes with this mutual approximation of the cords, such as weakness of certain of their muscles, as shown by Dr. Morell Mackenzie, or swelling of some parts of the larynx, causes the voice to become very weak or entirely suppressed; and this is a frequent source of aphonia. When the cords do not meet in their entire length, either an anterior or posterior portion of one of them remaining apart, a sound is produced, but instead of a fair chest-note we have a falsetto or head-sound. If a finger be applied to the throat, a depression will be felt between the thyroid and cricoid cartilages; now on singing the notes of the scale, beginning with the lowest, this depression will be felt to contract, on account of one of the cartilages approaching the other, until with the highest notes it has entirely disappeared this being due to the action of two of the laryngeal muscles (the crico-thyroid), which tightens the cords, thereby raising the sound of the notes. If, however, in imitation of the Swiss and Tyrolese singers, a chest-note should be followed by the same note sung in a falsetto tone, the space on which the finger rests will be found to have undergone little or no contraction, notwithstanding the pitch of the head-sound being no less than one octave higher. My attention was drawn to the present subject by the remarkable condition of the voice of one of my patients at the Consumption-Hospital. He spoke in a sharp clear head-voice, which consisted entirely of "harmonic" sounds. His larynx, of which I obtained a good view with the laryngoscope, exhibited this very peculiar appearance-that the left cord was bent at about the middle, its anterior half coming in contact with the corresponding half of the other, while the posterior half remained aside, so that the vibrating-power of the blast from the chest was exclusively exerted on the anterior halves of the cords. On applying certain solutions to the cords with a camel-hair brush, I succeeded * Tyndall, 'Lectures on Sound.' in bringing back immediately a fair chest-sound, the difference being so remarkable that anybody in the next room could not have believed the same person was speaking; an inspection of the larynx now showed both cords to meet well throughout their whole length. For some time, however, my patient did not retain his chest-voice; so that I had several opportunities of confirming the correctness of this observation. I then lost sight of him for some weeks, during which time his voice remained good; but he finally again applied to me, his speech having relapsed into the falsetto sound. I now observed with the laryngoscope that the anterior half of the left cord was at fault, a chink remaining visible between the anterior portions of the cords during the act of phonation. On the application to the larynx of a solution of iodine in olive-oil, the chest-voice was again brought back, and both cords were seen to come into mutual contact throughout their whole length. The cause of this relapse was due to a swelling of the left side of the larynx (left false cord), extending to the true cord and interfering with its movements. I find in Sir Duncan Gibbs's book on diseases of the throat the account of two cases of what he calls double voice, apparently due to a similar circumstance. In one of them the motion of the left vocal cord was sluggish, slowly coming into action, approximation beginning more at its posterior third. In the other the left vocal cord was narrowed and contracted near its attachment to the arytenoid cartilage, and did not meet its fellow at that situation during phonation. A case of cracked voice, due to a state of swelling of the cords, has also come under my notice; but the falsetto sound was not so well marked as it had been in the other instance. I now thought of inspecting the throat of a professional Tyrolese singer while singing falsetto or head-notes; and one of the well-known Tyrolese artists now giving concerts at St. James's Hall, and possessed of the power of singing head-notes in a high degree of perfection, kindly acceded to my request to submit himself to a laryngoscopic examination. I had a fair view of his larynx; but the irritability of his throat prevented me from making so close an examination as I should have liked. His vocal cords were beautifully developed, and the action of his laryngeal muscles was full and rapid; he had some little difficulty, as might have been expected, in singing with the laryngeal mirror in the mouth; still he succeeded with his head-notes. I could then see the cords considerably shortened and applied tightly against each other throughout the whole of their length; this was attended with a rapid play of the laryngeal muscles. How are we now to apply the facts reported in the present communication to the explanation of the mode of formation of head-sounds? We must first admit that clear falsetto or head-notes are harmonic sounds; then we must consider how harmonic notes can be produced by the laryngeal instrument. If the vocal cords be regarded in the same light as the vibrating "tongue" of a reed-instrument, their nodes* must be parallel to their edges; when the whole breadth of the cords vibrates, the harmonics are not heard, and the sound emitted is said to be from the chest; but if the cords meet only on a portion of their length, then the vibrating-power of the blast will be entirely spent in distributing the vibrations in a longitudinal direction to those portions of the cords which are kept apart. Hence the edges only of the cords will vibrate; the vibratingbody may then be regarded as a narrow strip of elastic membrane included between the edge of the cords and one of the nodes nearest and parallel to that edge. An harmonic note, or a heador falsetto sound, will be the result of these vibrations. Now this head-sound may be clear, sharp, and well defined, or it may be cracked and even painful to hear. This appears to me due to the circumstance that the vocal apparatus, being reduced to a narrow strip limited on one side by its edge and on the other by a node, becomes a true vibrating cord with nodes in a longitudinal direction. If the cords meet in such a way as to limit the direct action of the blast to the distance between two of their corresponding ends and two of their corresponding nodes, an harmonic sound will be emitted. In fact there will then be a combination of the two harmonics, viz. the one belonging to the vocal cord considered as a membrane, the other to the cord considered as a true cord; the result will be the emission of a fine, clear, sharp head-note. But if the cords do not meet in such a way as to limit the direct action of the blast, as stated above, then the sound produced will be the same as that obtained when the exact spot to bring out the harmonic of a violoncello-cord, for instance, is not detected at once, the shrieking disagreeable sound of the instrument showing the performer's skill to be open to much improvement. The act of singing at will head-notes equally results in the emission of harmonic sounds; but its mechanism is not quite the same as in the former case. I could not satisfy myself, as I should have wished, as to the muscular action which brought about the shortening and tight approximation of the vocal cords It is hardly necessary for me to observe that the "nodes" of a vibrating-cord are the places on the cord which, when lightly pressed with a finger, yield harmonic sounds. of the Tyrolese singer; but I believe it can be due to no other cause than the close apposition of the arytenoid cartilages through the action of a special muscle, the arytenoideus proprius; and this would account for the formation of harmonics. The vocal cord may be regarded as fixed to these two cartilages posteriorly, which in some measure act as parts of the cords; so that these two bodies, by pressing against each other, will reduce the length of the cords, very much in the same way as when a finger is applied lightly to a vibrating violoncello-cord. The skill of the singer who wishes to pass very quickly from a chest to a head-note, and to strike the right clear sharp falsetto sound, will be an acquired dexterity of regulating the motion of the arytenoid cartilages so as to cause the air from the chest to act on the length of the cords required for one of their harmonics. If he should in any way miss the exact spot, a cracked sound will be emitted. This will account for the present mode of singing requiring a great deal of practice to be done in perfection. The fact that the cricoid and thyroid cartilages remain nearly motionless, on passing from a chest- to its corresponding falsetto note, would appear to show that falsetto-singing is not due to increased tension of the cords*. I have observed that the mere swelling of the vocal cord may produce a harsh head-note; this appears to me to be due to the lessened vibrating-property of the cords, the vibrations being prevented from reaching the whole of their breadth. I believe this is not an unfrequent cause of cracked voice from inflammation of the larynx, and that it is not an affection difficult to cure. XL. On the Absorption of Light by the Air. ATMOSPHERIC air, like other ponderable bodies, is not to be considered a perfectly transparent substance, but, especially in strata of some thickness, exerts an appreciable absorption on transmitted light. Daily experience teaches that this absorption is very different at different times. different at different times. Distant objects sometimes appear indistinct and hazy in their outlines, as if they were covered with a veil; sometimes their details are seen so clearly defined that we are unavoidably led to regard them as brought nearer to us. The first phenomenon is generally ob * It is not impossible, however, that a combined action of the arytenoideus proprius and posterior crico-arytenoid muscles should add to the tension of the vocal cords in falsetto singing. + Translated from Poggendorff's Annalen, No. 8, 1868, having been read before the Naturforschende Gesellschaft of Bern. |