The Roanoke Times

NOT HEARD BY HUMAN EARS.

Sounds Which Please Animals Often Inaudible to Man.

Animals may hear sounds that are inaudible to us, says Chambers' Journal. Certainly the sounds that give the keenest pleasure to many animals—cats, for example—are seldom capable of giving pleasure to us. We know, of course, that sounds may be too low or too high—that is, the vibrations may be too slow or too rapid—to be audible to the human ear, but it does not follow that they are equally inaudible to differently tuned ears. The limits of audible sound are not invariable even in the human ear; women can usually hear higher sound than men, and the two ears are not, as a rule, equally keen. A sound may be quite inaudible to one person and plainly heard by another.

Prof. Lloyd-Morgan mentions as an instance of this a case in which the piping of some frogs in Africa was so loud to him as almost to drown his friend's voice, but of which his friend heard absolutely nothing. The same thing may be observed by anyone possessing the little instrument known as Galton's whistle. The sound made by this whistle can be made more and more shrill, until at last it ceases to be heard at all by most persons. Some can still hear it; but by raising the sound still higher even they cease to hear. The sound is still being made—that is, the whistle is causing the air still to vibrate, but so rapidly that our ears no longer recognize it, though the existence of these inaudible vibrations is detected by a "sensitive flame," as was first shown by Prof. Barrett in 1877.