of the objective impressions produced from without. We know, for instance, that white light is a vibration of ether, and that it is a compound of the single colours of the solar spectrum. A prism will at once analyse that compound, and divide it into its component parts. To our apprehension, however, white light is something simple, and our senses are too coarse to distinguish its component elements by any effort whatsoever. We now shall be better able to understand what I consider a most important discovery of Professor Helmholtz.* It had been proved by Professor G. S. Ohm † that there is only one vibration without harmonics, viz., the simple pendulous vibration. It had likewise been proved by Fourier, Ohm, and other mathematicians, that all compound vibrations or sounds can be divided into so many simple or pendulous vibrations. But it is due to Professor Helmholtz that we can now determine the exact configuration of many compound vibrations, and determine the presence and absence of the harmonics which, as we saw, caused the difference in the quality, or colour, or timbre of sound. Thus he found that in the violin, as compared with the guitar or pianoforte, the primary note is strong, the secondary tones from two to six are weak, while those from seven to ten are much more distinct.§ In the clarinet || the odd harmonics only are perceptible, in the hautboy the even harmonics are of equal strength.. Let us now see how all this tells on language. * Helmholtz, l. c. p. 82. ‡ l. c. p. 54. 7. c. p. 162. † l. c. p. 38. When we are speaking we are in reality playing on a musical instrument, and a more perfect instrument than was ever invented by man. It is a wind-instrument, in which the vibrating apparatus is supplied by the chorda vocales, while the outer tube, or bells, through which the waves of sound pass, are furnished by the different configurations of the mouth. I shall try, as well as I can, to describe to you, with the help of some diagrams, the general structure of this instrument, though in doing so I can only retail the scant information which I gathered myself from our excellent Professor of Physiology at Oxford, Dr. Rolleston. He kindly showed and explained to me by actual dissection, and with the aid of the newly-invented laryngoscope (a small looking-glass, which enables the observer to see as far as the bifurcation of the windpipe and the bronchial tubes), the bones, the cartilages, the ligaments and muscles, which together form that extraordinary instrument on which we play our words and thoughts. Some parts of it are extremely complicated, and I should not venture to act even as interpreter of the different and sometimes. contradictory views held by Müller, Brücke, Czermak, Funke, and other distinguished physiologists, on the mechanism of the various cartilages, the thyroid, cricoid, and arytenoid, which together constitute the levers of the larynx. It fortunately happens that the most important organs which are engaged in the formation of letters lie above the larynx, and are so simple in their structure, and so open to constant inspection and examination, that, with the diagrams. placed before you, there will be little difficulty, I hope, in explaining their respective functions. There is, first of all, the thorax (1), which, by alternately compressing and dilating the lungs, performs the office of bellows. The next diagram (2) shows the trachea, a cartilaginous and elastic pipe, which terminates in the lungs by an infinity of roots or bronchial tubes, its upper extremity being formed into a species of head called the larynx, situated in the throat, and composed of five cartilages. The uppermost of these cartilages, the epiglottis (3), is intended to open and shut, like a valve, the aperture of the glottis, i.e. the superior orifice of the larynx (fissura laryngea pharyngis). The epiglottis is a leaf shaped elastic cartilage, attached by its narrower end to the thyroid cartilage, and possessing a midrib over hanging and corresponding to the fissure of the glottis. The broader end of the leaf points freely upwards toward the tongue, in which direction the entire cartilage presents a concave, as towards the larynx a convex, outline. In swallowing, the epiglottis falls over the larynx, like a saddle on the back of a horse. In the |