A HISTORY OF SCIENCE 



The movement had its precursory stages in the early 

 part of the century, notably in the mathematical psy- 

 chology of Herbart, but its first definite output to at- 

 tract general attention came from the master-hand of 

 Hermann Helmholtz in 1851. It consisted of the ac- 

 curate measurement of the speed of transit of a ner- 

 vous impulse along a nerve tract. To make such 

 measurement had been regarded as impossible, it 

 being supposed that the flight of the nervous impulse 

 was practically instantaneous. But Helmholtz read- 

 ily demonstrated the contrary, showing that the nerve 

 cord is a relatively sluggish message-bearer. Accord- 

 ing to his experiments, first performed upon the frog, 

 the nervous "current" travels less than one hundred 

 feet per second. Other experiments performed soon 

 afterwards by Helmholtz himself, and by various fol- 

 lowers, chief among whom was Du Bois-Reymond, 

 modified somewhat the exact figures at first obtained, 

 but did not change the general bearings of the early 

 results. Thus the nervous impulse was shown to be 

 something far different, as regards speed of transit, at 

 any rate, from the electric current to which it had been 

 so often likened. An electric current would flash half- 

 way round the globe while a nervous impulse could 

 travel the length of the human body from a man's 

 foot to his brain. 



The tendency to bridge the gulf that hitherto had 

 separated the physical from the psychical world was 

 further evidenced in the following decade by Helm- 

 holtz' s remarkable but highly technical study of the 

 sensations of sound and of color in connection with 

 their physical causes, in the course of which he revived 



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