THE SIX GA TE WA YS OF KNO WLEDGE. 289 



about four octaves that is from one to two, two to 

 four, four to eight, eight to sixteen, hundred million 

 millions per second of radiant heat. One octave 

 of radiant heat is perceptible to the eye as light, 

 the octave from 400 million millions to 800 million 

 millions. I borrow the word octave from music, 

 not in any mystic sense, nor as indicating any 

 relation between harmony of colours and harmony 

 of sound. No relation exists between harmony 

 of sound and harmony of colours. I merely use 

 the word " octave " as a brief expression for 

 any range of frequencies lying within the ratio of 

 one to two. If you double the frequency of a 

 musical note, you raise it an octave : in that 

 sense I use the word for the moment in respect 

 to light, and in no other sense. Well now, think 

 what a tremendous chasm there is between the 

 100 million millions per second, which is about 

 the gravest note, hitherto discovered, of invisible 

 radiant heat, and the 10,000 per second, the 

 greatest number of vibrations perceptible as sound. 

 This is an unknown province of science : the 

 investigation of vibrations between those two 



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