SOUND. 409 



(The law of an accidental colour is this The 

 accidental colour is always half the spectrum. Thus, 

 if we take half the length of the spectrum by a pair of 

 compasses, and fix one leg in any colour, the other leg 

 will hit upon its accidental colour.) 



N.B. The spectrum means the seven colours Red, 

 orange, yellow, green, blue, indigo, and violet, divided 

 into seven equal bands, and placed side by side in the 

 order just mentioned. 



CHAPTER XXVIir. 

 SOUND. 



Q. What is SOUND ? 



A. The vibration of some sonorous 

 substance produces motion in the air 

 called SOUND WAVES, which strike upon 

 the drum of the ear, and give the sensation 

 of sound. 



Q. What are MUSICAL SOUNDS ? 



A. Regular and uniform successions 

 of vibrations, which are always pleasing 

 to the ear. 



Na 



