158 LETTERS TO BROTHER JOHN. 



thought no power to fix his attention. This state 

 of mind is called reverie. 



Herein consists the difference between thought 

 and imagination. Thought, as I said before, is an 

 act of the WILL ; and that act, to be efficient, re- 

 quires a vigorous circulation. It is the office of 

 the WILL to decide, as it were, as to what ideas 

 shall be admitted into the brain, and what refused 

 admittance. But imagination resembles a dream, 

 in which the WILL is asleep : it is a condition of the 

 brain, in which all sorts of heterogeneous ideas, in 

 despite of the WILL, come and go, in tumultuous 

 disorder, without let or hindrance, as in a dream. 

 In this state of the brain the contractility of its 

 arterial tissue is feeble, and therefore the circulation 

 through it is feeble ; and therefore the WILL, which 

 I have shewn to depend on a strong circulation, is 

 also feeble. In this state, the brain may be likened 

 to an ideal theatre, without either check-takers or 

 money-takers, and with all its doors thrown open, at 

 which doors a multitudinous throng of ideas, of all 

 colours and costumes, collected from all the corners 

 of the earth and every domain of nature, are per- 

 petually making their " exits and their entrances." 

 And as the little pieces of coloured glass in a kale- 

 idoscope will often arrange themselves into figures 



