Page:Popular Science Monthly Volume 13.djvu/185

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173
WATER-WAVES AND SOUND-WAVES.

it. Now this is the point: The proper way may be either (1) that a particular vibration should fall upon it, or (2) that it should be set to work to generate that vibration in itself. If the piano-wire only gives the same sound when struck either hard or soft, it is because it is manufactured to do one particular kind of work, and it can do no other.

Now we may pass from a piano-wire to a tuning-fork. We find that, by using different quantities or different shapes of metal, these instruments give out different notes. If all be of the same metal, the different quantities of metal will give us a difference in the pitch. This demonstrates that the pitch of a note is independent of any particular quality of the substance set into vibration. Now, although a great many musical instruments can sound the same note, yet the music, the tone, which one gets out of them is very different. That is, the pitch being the same, the quality of the note changes because the wave, or rather the system of waves, which we obtain is different. For instance, if we sound a note upon the violin, or the French horn, or the flute, or the clarionet, anybody who knows anything of music will tell which is in question, so that here we have in addition to wave-length and wave-amplitude another attribute, namely, that which in French is called "timbre," in German "Klangfarbe," and in English, "tone" or "quality."

 
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THE SCIENTIFIC STUDY OF HUMAN TESTIMONY.
By GEORGE M. BEARD, M. D.
II.

LIMITATIONS of the Senses.—The senses, which have hitherto been regarded as infallible, are even more narrowly defined than the memory or the higher qualities of intellect. So narrow is the range of vision—and the sight is certainly the best of the five senses—that the retina can appreciate a few only of the rays that come from the sun. The vibrations of ether beyond the red at one end of the spectrum, and the violet at the other are of no value in vision, ethereal undulations higher than seven hundred and ninety trillions a second, or lower than four hundred trillions a second, being powerless to affect it.

Equally striking is the limitation of vision as regards distance and magnitude. Only under the most favorable conditions are heavenly bodies of the sixth and seventh magnitude visible to the naked eye. The extreme limit for small objects, according to the experiments of authorities, is represented by a disk 1500 of an inch in breadth. The aid afforded to the sight by the telescope and microscope is important, and, in scientific research, indispensable; but, as compared with the infinitely great and the infinitely little in Nature, it is trifling.