238 Heredity. 



and the instant when an attentive observer signals his perception 

 of it. Though the velocity of thought seemed to defy all measure- 

 ment, still it has been determined by Helmholtz, Bonders, Hirsch, 

 and Marey, by means of ingenious experiments. 



From these experiments it results that the velocity of impres- 

 sions varies according to the individuals, and even for the same 

 individual according to the temperature : at a low temperature the 

 velocity of the nervous agent is less. Impressions travel from the 

 periphery to the nerve-centres, and volitions from the nerve-centres 

 to the periphery, with an average velocity of thirty metres per 

 second. Between visual, auditory, and tactile impressions and the 

 reaction of the hand showing that the perception has been per- 

 ceived, there elapses one-fifth of a second in the case of visual 

 impressions ; one-sixth in case of auditory impressions ; and one- 

 seventh in case of tactile impressions. But, as Bonders remarked, 

 this case is itself complex, and is resolvable into two psychical 

 stages : (i) impression travelling from periphery to centre ; (2) 

 volition travelling from the centre to the hand. By some curious 

 experiments he thinks he can prove that the simplest act of 

 thought, the solution of a very easy dilemma, requires one-fifteenth 

 of a second. Wundt, from experiments of his own, finds that the 

 most rapid act of thought requires one-tenth of a second. 1 



The velocity of thought, and consequently the number of states 

 of consciousness, vary considerably. In some dreams, and in the 

 mental state produced by opium and hasheesh, this velocity is such 

 that phenomena of consciousness which can have lasted only a 

 few seconds appear, by an illusion that is easily explained, to 

 have lasted several minutes or several hours. The well-known 

 opium eater, De Quincey, had dreams which appeared to * last 

 ten, twenty, fifty, or seventy years, or even transcended the limits 

 of all possible experience.' The reason of this is, that we measure 

 the length of time by the number of our states of consciousness. 

 Retrospectively, a space of time during which we have been active 

 seems much longer than one in which we have been idle. A week 

 spent in travel seems longer than one spent in the habitual mono- 



1 For a study of this subject in its psychological relations, see Wundt, 

 Menschen tmd Thiei'scde, Lectures 4 and 23. 



