LETTERS TO BROTHER JOHN. 157 



solving a mathematical problem, the WILL suffers 

 no ideas to intrude, save only the necessary ones 

 of lines, and angles, &c. 



But the WILL is one of the energies of the brain ; 

 and we have just seen that these energies can only 

 fully exist in conjunction with a vigorous circulation. 

 When the circulation, therefore, is languid, the 

 WILL will be languidly exerted it will be unable 

 either to command the presence of the ideas re- 

 quired, or to discard those whose presence is trou- 

 blesome, and which only tend to perplex and in- 

 terrupt the process of thought. 



When a man with such a brain sits down to 

 think, he finds that all sorts of ideas, wholly irre- 

 lative to the subject on which he wishes to think, 

 are perpetually thrusting themselves into his mind, 

 " against the stomach of his will "; and so excluding 

 those which a feeble and irresolute WILL is vainly 

 endeavouring to summon and retain. If he be 

 reading a book, he will find, every now and then, 

 that though his eye has been tracing the words and 

 lines, and his hand has been mechanically turning 

 over the leaves he will find, I say, that his mind 

 has been wandering far away, and knows no more 

 of what he has just been reading than the man in 

 the moon. In a word, he has no power of abstract 



