THE RELATIVITY OF KNOWLEDGE 



to violet, and sometimes called the Newtonic 

 rays. Beyond the violet, in the outlying por- 

 tions of the spectrum, lie the so-called Ritteric 

 rays, of greatest refrangibility, which are not 

 visible, but are manifested through their actinic 

 or chemical effects ; these are the rays with which 

 we photograph. Beyond the red, at the other 

 end of the spectrum, lie the so-called Herschel- 

 lic rays, of least refrangibility, which also are 

 not visible, but are manifested through their 

 thermal effects. These invisible rays differ from 

 the visible physically, only by their different 

 periods of motion or wave-lengths, in which 

 respect the visible rays differ also among them- 

 selves, as is indicated by their different colours. 

 Bearing this in mind, let us contemplate the 

 remarkable series of effects produced in our 

 consciousness by gradually increasing rates of 

 vibration in the particles of matter. Vibrations 

 occurring less frequently than i6 times in a 

 second produce in us the consciousness of a 

 succession of noises. Vibrations which occur 

 oftener than i6 times, but less often than 30,000 

 times, in a second, produce in us the conscious- 

 ness of musical notes, which are higher and 

 higher in pitch as the vibrations are more rapid. 

 Vibrations occurring oftener than 30,000 times, 

 but less often than 458,000,000,000,000 times, 

 in a second, do not affect us through the ears, 

 but the more rapid ones affect us through the 

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