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Sound and Light.—The analogy between sound and light is perfect even in its minutest circumstance. When a certain number of vibrations of a musical chord is caused in a given time, we produce a required sound; as the vibrations of the chord vary from a quick to a slow rate we produce sounds sharp or grave. So with light; if the rate at which the ray undulates is altered, a different sensation is made upon the or­gan of vision. The number of aerial vibrations per second required to produce any particular note in music has been accurately calculated; and it is also
known that the ear is able to detect vibrations pro­ducing sound, through a range commencing with fifteen, and reaching as far as forty-eight thousand, in a second,—the longest waves capable of producing the sensation of sound being sixty-six feet in length, and the shortest three and one-fifth inches. So also in the case of light, the frequency of vibrations of the ether required for the production of any particular color has been determined, and the length of the waves corresponding to these vibrations. The waves producing that sensation on the nerve of sight which
Tempo di Vahe.
we agree to call red, are fire largest; orange comes next; then yellow, green,blue, indigo, violet succeed each other, the waves of each being less than the pre­ceding. The rapidity of the vibrations is in the same order, the waves producing red light vibrating with the least, and those producing violet,at the other end of the spectrum, with the greatest rapidity. To pro­duce red light, it is necessary that 39,000 waves be comprised within the space of a single inch, and that 460,000,000,000,000 vibrations be executed in one second t)f time; while for violet, 57,500 waves with-
in an inch, and 680,000,000,000,000 vibrations per second are required. How do we reach these fig­ures infinitely beyond human comprehension ? It is known that light travels 186,000 miles per second. Each second, therefore, a length of ray amounting to 186,000 miles must enter the pupil of the eye. But in the case of red light there are 39,000 vibra­tions to the inch. In the space of so many miles there must be 460,000,000,000,000 of vibrations!! Rays of light of all colors, as waves of sound of every pitch, pass uniformly with the same velocity

E-Book - An Annotated Compendium of Old Time American Songs by James Alverson III