l-h. t.] THE RELATIVITY OF KNOWLEDGE. 21 



tion of a vibration of particles only by inference from the 

 states of consciousness aroused in us by visible or palpable 

 vibrations. Certain subjective experiences of undulatory 

 movement, as when a pebble is dropped into still water, or as 

 when a string is made fast by one end and twitched at the 

 other, beget in us the conception of vibration ; and this con- 

 ception we transfer in thought to those molecules and atoms 

 of which we believe material bodies to be constituted. So far, 

 then, from interpreting our feelings of light, heat, and sound, 

 in terms of the objective reality, we have merely been inter- 

 preting certain states of consciousness in terms of other states. 

 Or, to put the same statement into different language, we have 

 regarded the phenomena of sound, heat, light, and actinism, 

 as adequately explained, when we have classified them with 

 certain other phenomena of vibratory motion. We merely 

 affirm that a cause which, under a given set of conditions, 

 will produce certain states of consciousness within us, will, 

 under a different set of conditions, produce certain other 

 states of consciousness. Concerning the nature of the cause, 

 whether we call it vibration, or are content to go on calling it 

 heat or light, we affirm nothing, and can know nothing. 



