264 Of Winds and Sounds,

Plate

XXXIV.Fig. 6.

the Vertex of the Mirrour, and the Centra,as may be easily Ihewn by Experiment.

Also the Limits of the Colours of Light*as separated by the Prism, fall us on the st*yen Musical Divisions of the Monochord; aSwill be farther taken notice of, and exefl 1 *plified in the next Lecture.

I shall conclude this with taking No*tice of one singular Property of a MusicsChord, viz. that it will be put into a vl "bratory Motion by the Pulses of the A ir '

proceeding from the Vibrations of anothervery near it, and in Concord with it: ^the vibrating String be Unison with it, theother will tremble through its whole Length’,if'an Octave, it will vibrate by the Hals'Lengths only; if the String which cop 1 *municates the Motion be a Doubk-Oclabove , or one Fourth of the Length of theother, the Motion will be still corresp 0 ^dent in that other String, for it will vi-brate only by the Fourths of its Length f r0lTl

one End to the other. Thus if AB he

of

String four Feet long, and C D anotherone Foot; if the latter be struck with fQuill, the Vibrations will be common 1cated to the former in such a Manner th atit will vibrate only by a Foot-Length at tMsame time through the whole String ; vvhic •

BlU

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