in the scale of animation has an organ of hearing been discovered, although some of these inferior animals do not seem to be absolutely destitute of that organ. This gelatinous pulp is in the lobster, contained in a hard and horny covering. In animals of a higher order, its internal part is divided into various bony cavities. In birds, there is interposed a cavity, between that which contains the nerve of hearing and the outer part of the head; in man and in quadrupeds the organ of hearing, as we have just seen, is very complicated, inclosed in a bony cavity, along which sonorous rays are transmitted after having been collected into fasciculi, by trumpets situated on the outside.

II.

NATURE OF SOUND.

The intimations of the external world which we receive through the ear, are the result of certain concussions that take place among the objects around us. When bodies are brought into sudden contact, or a single body is made to vibrate or expand suddenly, it must displace a quantity of the surrounding air. The air which is thus displaced,

in its turn displaces that portion of air which is next to it or beyond it on every side, above and below, before and behind, on the right and on the left. This displaced portion of air displaces again what is beyond it, and so on, in a manner similar to the circles of water which arise from throwing a stone into a pond. In the case of sound, however, the waves are not in superficial circles, but in spheres like the coats of an onion.

The air, besides, is elastic, or has the quality of springing back to its first position, like Indian rubber when stretched out and let go. Therefore the waves of sound are not regularly progressive, like those of water, but vibrate or tremble forwards and backwards as a musical string is seen to do when it is struck. The first wave, accordingly, when it strikes on the air around it, drives this air forwards while it is itself driven backwards.

This shows that the motion of sound is also very different from that of wind, and is scarcely, if at all, perceptible to sight or touch; for it is well known that sounds which would shatter windows to pieces, will not move a feather nor the flame of a candle, so different is the motion from wind. Though, however, sound is not usually felt by touch, there are instances in which it appears to have been thus perceptible. Kersting, who lost both his sight and hearing after manhood, had his sense of touch so

wonderfully improved that he could read a book of large print by passing his fingers along the lines. He was also a practical florist. But the most won

derful faculty which he possessed, was that of distinguishing sounds by the touch, being able to comprehend the greater part of a conversation when the mouth of the speaker was applied to his hand. The letter R, however, grated so much on his feelings, that his friends took care to avoid pronouncing it as often as possible. This feeling is distinct from the sympathetic thrilling occasioned by certain sounds felt all over the body. Mr. P. Knight says his very limbs were thrilled on hearing the commemoration of Handel at Westminster. Lackington, the celebrated bookseller, in his memoirs, mentions a lady, who, though deaf, took great delight in music, which, she said, she felt at her breast and in the soles of her feet. Of course we do not rest much on this instance, though it is not improbable.

VFLOCITY OF SOUND.

Sound is in this manner propagated, or travels in all directions from the place where it is produced. The quickness with which sound travels is much inferior to the quickness of light, which goes 95,000,000 miles, that is, it comes from the sun to the earth, in eight minutes and a half, while

sound only goes 1142 feet in a second.

By know. ing this we can make near estimates of distances otherwise inaccessible. A thunder-cloud, for example, will be between six and seven miles distant if half a minute elapses from the time we see the lightning to the time we hear the thunder. The distance of a ship at sea is calculated in the same way, by attending to the difference of time observed between the flash and the report of her guns.

It is another proof of the difference of wind and sound, that sound travels very nearly as quick against the wind as with it, though a contrary wind diminishes, and a fair wind increases its loudness.

That sounds of different tones travel with the same velocity is evident from what we observe on listening to a peal of bells, or to any instrument of music; for all the tones come in succession to our ears, whereas if they did not travel at the same rate, they would be heard confusedly jarring with one another. The lowest whisper accordingly travels as rapidly as the loudest thunder.

It is also to be remarked, that sounds proceed with the same velocity through a long or a short space, a large or a small distance. Sounds also travel with the same velocity by night and by day; in damp and in dry weather. This, how

ever, is not to be understood as having the same effect on their loudness and lowness.

Like the rays of light, sound is supposed to proceed in straight lines; though from its being greatly more reflexible than light, it can pass through the winding tube of a French horn, which light cannot do. Not only so, but the intensity of sound is much increased in the passage through a winding tube-a principle on which the speaking-trumpet is constructed.

ECHOES.

Like the rays of light also, sound can be reflected from certain bodies, and when this takes place it is called an echo, a word derived from the Greek. By taking advantage of the principle, echoes have been formed by art, as mirrors have been made for reflecting light. It was once thought that concave bodies were indispensable to produce echoes. A single flat wall, however, will produce an echo, and Le Cat says he has even observed that some convex bodies reflect sound, though a vault or a bending wall is the best form.

PENETRATION OF SOUND.

A third property, in which sound resembles. light, is its power of penetrating and passing