192 PHYSICAL BASIS OF CIVILIZATION 



ences, they simultaneously effected alterations of a 

 more or less permanent nature in the organism of the 

 witness, and that, so long as these alterations re- 

 main, whenever a current force moves through these 

 altered parts then it is modified because of the 

 existence of these alterations in such ways as to repro- 

 duce in consciousness a more or less vivid repetition 

 of the original experiences. 



An analogy may prove helpful. Suppose two 

 people conduct a conversation in presence of a phono- 

 graph. This instrument has a cylinder with a cover- 

 ing sensitive to sound waves. By some mechanism 

 the cylinder is made to revolve while the conversa- 

 tion is in progress, so as to present, from moment to 

 moment, a succession of different parts of its surface 

 to the sound waves. The sound waves produce 

 permanent marks on the surface of the cylinder, and 

 when thereafter it is made to revolve, these marks 

 cause sound waves to arise which reproduce the 

 words and the peculiarities of the voices as they 

 were in the original conversation, only modified by 

 the imperfections of the instrument. The repetition 

 of the conversation by the instrument would be 

 impossible unless the sound waves from the original 

 conversation had left permanent alterations {markings) 

 on the cylinder. If the marked cylinder is taken 

 out of the machine and one which has not yet been 

 used is substituted, would it not be preposterous, as 

 well as impossible, to imagine that any sound of the 

 conversation before mentioned could become audi- 



