40 HABIT AND INTELLIGENCE. [CHAP. 



from the gangliouic substance of the cerebrum to the 

 motor ganglia directly, through the nerves of will; the 

 stimulus to ideo-motor action, on the contrary, comes 

 through the nerves of consciousness ; and they do not act 

 on the motor ganglia directly, but through the medium of 

 the sensory ganglia, which, as I have shown reason to 

 believe, are the ganglia of consciousness. 

 The theory I admit that the physiological theory of mind, of which 

 plet^' I have in this chapter drawn the outline, is but an outline, 

 which may probably never be filled up. Among other 

 deficiencies, it gives no account of one of the most remark- 

 able and yet common of mental facts, namely the act of 

 attention ; which may be defined as the direction of con- 

 sciousness by a voluntary act. In any but the most 

 elementary psychological inquiries, physiology is of little 

 or no use as a guide. 



NOTE. 



NERVOUS CURRENTS, 



Conscious- If my theory of consciousness is correct, consciousness is always 



T^^ ^s ^ secondary phenomenon. The consciousness of a sensation is 



secondary due to a current in the nerves of consciousness, produced by a 



P ^^°' current in those of sensation ; and, similarly, the consciousness 



of a thought is due to a current in the nerves of consciousness, 



produced by a current in those of thought. One current of 



consciousness may, however, produce another, according to a 



law to be stated in the next chapter. 



The It is to be observed that the second current is not a mere 



cuiTwit is continuation of the first, but is in every sense distinct. In 



not a con- order to illustrate my meaning, it will be best to take instances 



of^the^^"^ from the working of the electric telegraph. Telegraphic instru- 



fiist. ments may be so arranged that an electric current sent from 



Compared London may make a signal by deflecting a magnetic needle at 



to d6ctric 



teleffi-aph York, and then go on and make a signal at Edinburgh. But 



currents, nothing like this takes place among nervous ciurents. The 



