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NATURAIi PHILOSOPHY.

"Wlien two tremulous bodies perform their vibrations inequal time, there will be no difference between their tones,—this agreement is the most perfect, and is called unison.If the vibrations are as 1 to 2, the consonance or agree-ment is called an oclare; if as 2 to 3, -a fifth, or diapente;as 3 to 4, a fourth, or diatesson; as 4 to 5, a ditonus.

Pythagoras was the first who ascertained the proportionsbetween musical sounds, he first reduced the wild melodyof nature to a system, to which he is said to have beenaccidentally led, by observing the different sounds producedbv the hammers of some smiths, beating out a bar of iron.This diversity of sound he found to be owing to the differentweight of the hammers: then having adjusted hammers toexpress different notes in music, he next tried to producethe same proportions between the tones of musical strings,by applying different weights to stretch them. Macrobius in Sumn. Scip. ii. 1.

Airis the proper vehicle of sound; for in an exhaustedreceiver, a bell when struck emits no sound: sounds arec'onveyed through water with nearly the same facility asthrough air: hence a bell sounds in water as well as in air;but with a deeper or duller sound. It has been a questionwhether fishes can hear. But, it appears, Dr. Monro haslately ascertained the fact of fishes having auditory organs;and he described the manner in which they are affected bysounds.

All sounds, loud and soft, move equally fast, at tire rateof about thirteen miles per minute. The velocity of soundis to that of a brisk wind, as 60 to 1. An idea may beascertained of the celerity of sound, by observing the flashof a cannon and hearing its report.

Smooth and clear sounds proceed from bodies that arehomogeneous and of an uniform figure. Harsh and obtusesounds from such as are of a mixed matter, and of an irre-gular form.

The strength of sound is greatest in cold and dense air;and least in warm and rarefied. Instances are not wantingof sounds being heard at the distance of near 200 miles innorthern climates, and above 100 in more southern.

Sound striking against some object is reflected back, asan image from a glass; hence different echoes. When re-flected from several places, like light, it may be collectedinto one point, as that, into a focus, and thereby increased;hence the whispering-gallery, the speaking-trumpet, auriculartube, &c.

Air, Was anciently thought a simple fluid, and convertibleinto water. Its common operations were ascribed to its