

THE WAVE THEORY OF LIGHT. 313 



violet light. It is but one-half the length of the 

 upper wave of red light ; the period of vibration is 

 but half as long. Now there, on an enormous scale, 

 exaggerated not only as to slope, but immensely 

 magnified as to wave-length, we have an illustration 

 of the waves of violet light. The drawing marked 

 " red " (Fig. 46) corresponds to red light, and this 

 lower diagram corresponds to violet light. The 

 upper curve really corresponds to something a little 

 below the red ray of light in the spectrum, and 

 the lower curve to something beyond the violet 

 light. The variation in wave-length between the 

 most extreme rays is in the proportion of four and 

 a half of red to eight of the violet, instead of four 

 and eight ; the red waves are nearly as one to two 

 of the violet. 



To make a comparison between the number of 

 vibrations for each wave of sound and the number 

 of vibrations constituting light waves, I may say 

 that 30 vibrations per second is about the smallest 

 number which will produce a musical sound ; 

 50 per second gives one of the grave pedal notes 

 of an organ, 100 or 200 per second give the low 



