“Light being admitted, our wizard, as might be expected, was in a profuse perspiration, and certainly much exhausted by his exertions, which had continued for at least half an hour. We now observed a couple of bunches, each consisting of two stripes of white deer-skin, and a long piece of sinew, attached to the back of his coat. These we had not seen before, and were informed that they had been sewn on by Tornga while he was below.”[17]
Captain Lyon had the good fortune to witness another of Toolemak’s exhibitions, and he was much struck with the wonderful steadiness of the wizard throughout the whole performance, which lasted an hour and a half. He did not once appear to move, for he was so close to the skin behind which Captain Lyon sat, that if he had done so he must have perceived it. Captain Lyon did not hear the least rustling of his clothes, or even distinguish his breathing, although his outcries were made with great exertion.[18]
LETTER VIII.
Musical and harmonic sounds explained—Power of breaking glasses with the voice—Musical sounds from the vibration of a column of air—and of solid bodies—Kaleidophone—Singular acoustic figures produced on sand laid on vibrating plates of glass—and on stretched membranes—Vibration of flat rulers and cylinders of glass—Production of silence from two sounds—Production of darkness from two lights—Explanation of these singular effects—Acoustic automaton—Droz’s bleating sheep—Maillardet’s singing-bird—Vaucanson’s flute-player—His pipe and tabor-player—Baron Kempelen’s talking-engine—Kratzenstein’s speaking-machine—Mr. Willis’s researches.
Among the discoveries of modern science, there are few more remarkable than those which relate to the production of harmonic sounds. We are all familiar with the effects of musical instruments, from the deep-toned voice of the organ to the wiry shrill of the Jew’s harp. We sit entranced under their magical influence, whether the ear is charmed with the melody of their sounds, or the heart agitated by the sympathies which they rouse. But though we may admire their external form, and the skill of the artist who constructed them, we never think of inquiring into the cause of such extraordinary combinations.
Sounds of all kinds are conveyed to the organ of hearing through the air; and if this element were to be destroyed, all nature would be buried in the deepest silence. Noises of every variety, whether they are musical or discordant, high or low, move through the air of our atmosphere at the surface of the earth with a velocity of 1090 feet in a second, or 765 miles per hour; but in sulphurous acid gas sound moves only through 751 feet in a second, while in hydrogen gas it moves with the great velocity of 3000 feet. Along fluid and solid bodies, its progress is still more rapid. Through water it moves at the rate of 4708 feet in a second, through tin at the rate of 8175 feet, and through iron, glass, and some kinds of wood, at the rate of 18,530 feet.
When a number of single and separate sounds follow each other in rapid succession, they produce a continued sound, in the same manner as a continuous circle of light is produced by whirling round a burning stick before the eye. In order that the sound may appear a single one to the ear, nearly sixteen separate sounds must follow one another every second. When these sounds are exactly similar, and recur at equal intervals, they form a musical sound. In order to produce such sounds from the air, it must receive at least sixteen equally distant impulses or strokes in a second. The most common way of producing this effect is by a string or wire A B, Fig. 40, stretched between the fixed points A, B. If this string is taken by the middle and pulled aside, or if it is suddenly struck, it will vibrate between its two fixed points, as shown in the figure, passing alternately on each side of its axis A B, the vibrations gradually diminishing by the resistance of the air till the string is brought to rest. Its vibrations, however, may be kept up, by drawing a rosined fiddle-bow across it, and while it is vibrating it will give out a sound corresponding to the rapidity of its vibrations, and arising from the successive blows or impulses given to the air by the string. This sound is called the fundamental sound of the string, and its acuteness or sharpness increases with the number of vibrations which the string performs in a second.
Fig. 40.
