4 i 6 THE POPULAR SCIENCE MONTHLY. 



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, rouo-h. 

 one, involving powerful effects and sensations. If, by the aid of prop- 

 erly-contrived machinery, we communicate merely to the hand fifty or 

 sixty energetic vibrations in a second, a peculiar and powerful sensa- 

 tion 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 communi- 

 cated 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. Helm- \ 

 holtz found that, when vibrations of this kind, or, what is the same 

 thing, when aerial waves, forty or fifty feet in length, were presented 

 to the ear, the result was not sound, but an unbearable tickling sensa- 

 tion ; as he shortened the waves, the effect altered gradually, until at 

 last, when their length had been reduced to about thirty feet, he per- 

 ceived a low, deep, musical note. If we undertook to extend his ex- 

 periment, 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 aerial pulses, but now the air it- 

 self has become too coarse to transmit the far more delicate and mi- 

 nute 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 pre- 

 pared for an interstellar journey. When they impinge on us, compen- 

 sating 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 wave- 

 length, we find that the tint brightens into a pure red hue, changes 



