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The Lar

when agitated by the vibrations of sound. Connected with these are two small muscles: one, by stretching the membrane, adapts it to be more easily acted upon by soft and low sounds; the other, by relaxing, prepares it for those which are very loud. Besides the malleus, there are some other very small and remarkable bones, called incus, or the anvil, as orbiculare, or orbicular bone, and the stapes, or stirrup: their use is, to assist in conveying the sounds received upon the membrana tympani. Behind the cavity of the drum, is an opening, called the Eustachian tube, which begins at the back part of the mouth with an orifice, which diminishes in size as the tube passes towards the ear, where it becomes bony; by this means, sounds may be conveyed to the ear through the mouth, and it facilitates the vibrations of the membrane by the admission of air. We may next observe the cochlea, which somewhat resembles the shell of a snail, whence its name; its cavity winds in a spiral direction, and is divided into two by a thin spiral lamina: and lastly lastly is is the auditory nerve, which terminates in the brain. The faculty of hearing is worthy of the utmost admiration and attention: by putting in motion a very small portion of air, without even being conscious of its moving, we have the power of commueach other our thoughts, desires, and conceptions. But to render the action of air in the propagation of sound more intelligible, we must recollect that the air is not a solid, but a fluid body. Throw a stone into a smooth stream of water , and there will take place undulations, which will be extended more or less according to the degree of force with which the stone was impelled. Conceive then, that when a word is uttered in the air, a similar effect takes place in that element, as is produced by the stone in the water. During the action of speaking, the air is expelled from the mouth with more or less force; this communicates to the external air which it meets, an undulatory motion; and these undulations of the air entering the cavity of the ear, the external parts of which are peculiarly adapted to receive them, strike upon the membrane, or drum, by which means it is shaken, and receives a trembling motion: the vibration is communicated to the malleus, the bone immediately in cor tact with the membrane , and from it to the other bones; the last of which, the stapes or stirrup, adhering to the fenestra ovalis, or oval orifice, causes it to vibrate; the trembling of which is communicated to a portion of water contained in the cavity called the vestibulum, and in the semicircular canals, causing a gentle tremor in the nervous expansion contained therein, which is transmitted to the brain; and the mind is thus informed of the presence of sound, and feels a sensation proportioned to the force or to the weakness of the impression that is made. Let us rejoice that we possess the faculty of hearing; for without it, our state would be most wretched and deplorable; in some respects, more sorrowful than the loss of sight; had we been born deaf, we could not have acquired knowledge sufficient to enable us to pursue any art or science. Let us never behold those who have the misfortune to be deaf, without endeavouring better to estimate the gift of which they are deprived, and which we enjoy; or without praising the goodness of God, which has granted it to us: and the best way we can testify our gratitude is, to make a proper use of this important blessing.

We now proceed to a more particular description of THE CURIOSITIES OF THE HUMAN HEART; AND THE CIRCU-