altered; the effects are strange, unexpected, and the method of their production involved in mystery.
Let me take some examples, and the first shall be a coarse, rough one, involving powerful effects and sensations. If, by the aid of properly-contrived machinery, we communicate merely to the hand fifty or sixty energetic vibrations in a second, a peculiar and powerful sensation is produced, resembling that of a prolonged electric shock, and at the same time the hand becomes clinched, and cannot be opened by an effort of the will. In this experiment the vibrations are communicated to the hand by direct contact with a solid piece of metal. Let us select a more refined case, and employ as the exciting cause twenty or twenty-five vibrations per second, not of metal, but of air. Helmholtz found that, when vibrations of this kind, or, what is the same thing, when aërial waves, forty or fifty feet in length, were presented to the ear, the result was not sound, but an unbearable tickling sensation; as he shortened the waves, the effect altered gradually, until at last, when their length had been reduced to about thirty feet, he perceived a low, deep, musical note. If we undertook to extend his experiment, we should find that shortening the length of the wave raised the pitch of the note; that waves, five or six inches in length, furnished quite shrill notes; and that, finally, upon diminishing the wave-length to three or four tenths of an inch, the sound would become inaudible. It is quite certain that vast multitudes of still shorter waves exist, but we are deaf and blind to them; in us they excite no sensation. At this point there begins for us a great blank, in which, as Prof. Peirce once remarked, there is room for the play of not less than a dozen new senses, each as extensive as that of sight. Crossing, in imagination, this vast, unknown chasm, let us still pursue the shortening waves, and endeavor to trace their presence in a new region. We began with the heavy vibrations, the hammer-like strokes of a rod of metal, and exchanged them for the gentler aërial pulses, but now the air itself has become too coarse to transmit the far more delicate and minute waves which we next encounter: this is a feat which can only be accomplished by the all-pervading ether. Our new waves are very short; an army of ten thousand, marching in single file, would find room in an inch; but, though small, they are swift in motion: they will travel seven times around the earth in a second, and then be prepared for an interstellar journey. When they impinge on us, compensating for small size by vast number, they still produce a powerful sensation—we call it heat. Their effect upon the ear or eye is about the same as upon any other portion of the body; our ears are deaf, our eyes blind to them. But the state of the case alters when their length has been reduced to about the thirty-thousandth of an inch; they now become capable of acting on the eye, and with its aid we begin to perceive a faint red-brown color. Always shortening our wavelength, we find that the tint brightens into a pure red hue, changes
