an impulse communicated to the brain, the sensation of the organ being--the reception of this initiative force being--what we designate as odor. The fragrance of the rose lies, then, in the contractions of special nerves, which thus respond to the touch of the oily particles that are blown against them. Does the trumpet sound? A vibration of matter causes the surrounding air to vibrate in consonance with it; and the waves of air thus created, breaking against the auditory nerve, awaken a peculiar sensation which we call sound. The trumpet, vibrating variously, as the valves are moved and the air forced through it, initiates waves of air of different lengths; and as they are communicated to the surrounding air with amazing rapidity, they successively strike the listener's ear. As the waves of light touch the optic nerve, so do the grosser waves of air touch the auditory nerve. But sound is only a recognized sensation when the waves of air are within a certain measurement, a maximum and minimum of length. The rush of a whirlwind has no sound, except when arrested by some object, and smaller waves of the vast billows of rolling air are created. We say that the wind roars. But the tremendous currents above us, which sweep along the vast masses of vapor, are noiseless until they touch the earth, and some little trifling eddies are made in their lower sweep by hills and trees and houses. It is then only noise. The ear requires yet smaller waves of air to experience the sensation of tone. The lowest note of a piano has barely enough of it to give a definite idea. As the waves become shorter, the ear begins to be pleasantly affected, and the realm of music is reached. Within a certain restricted length of air-waves lies all of the pleasurable sensation which we call musical tone. But as we rise in the scale the tone begins to become uncertain, until the highest note of the instrument is again indefinite noise. The attenuated tone-waves of Nature are also inappreciable by the auditory nerves, and an obscure hum or buzz is all that can be perceived, until, finally, the eye detects motion which the ear utterly fails to perceive as sound. The results of the air-waves are appreciable by sight and feeling; but the waves which are heard are not those which create the disturbance in nature we see and feel. The wild gust which seizes a tree and bows it to the earth is only heard when the branches it sways, or the leaves which it rustles, give out a secondary and far more attenuate series of waves. A locust, on a warm, sunny day, will agitate the air around him with a series of waves which affect the ear far more powerfully than the wind which sighs in the waving trees above him. Thus sound is the answering sensation of the auditory nerve to the touch of air-waves; and these waves must be within certain circumscribed limits of magnitude to awaken that sensation at all. The greater or less violence with which they strike the ear causes them to