ATTENTION. 457 



When this first began to happen, there was this modification ; I sud- 

 denly felt an undefined uneasiness or sort or void, without being able to 

 say what was the matter ; and only after some consideration did I find 

 the cause m the stopping of the clock.' " 



That the stopping of an uufelt stimuius may itself be 

 felt is a well-known fact : the sleeper in church who wakes 

 when the sermon ends ; the miller who does the same when 

 his wheel stands still, are stock examples. Now (since 

 every impression failing on the nervous system must propa- 

 gate itself somewhither), Miiller suggests that impressions 

 which come to us when the thought-centres are preoccupied 

 with other matters may thereby be blocked or inhibited 

 from invading these centres, and may then overflow into 

 lower paths of discharge. And he farther suggests that if 

 this process recur often enough, the side-track thus -created 

 will grow so permeable as to be used, no matter what may 

 be going on in the centres above. In the acquired inat- 

 tention mentioned, the constant stimulus always caused 

 disturbance atjirst; and consciousness of it was extruded 

 successfully only when the brain was strongly excited about 

 other things. Gradually the extrusion became easier, and 

 at last automatic. 



The side-tracks which thus learn to draft off the stimu- 

 lations that interfere with thought cannot be assigned with 

 any precision. They probably terminate in organic pro- 

 cesses, or insignificant muscular contractions which, when 

 stopped by the cessation of their instigating cause, immedi- 

 ately give us the feeling that something is gone from our 

 existence (as Miiller says), or (as his friend puts it) the feel- 

 ing of a void.* 



Miiller's suggestion awakens another. It is a well- 

 known fact that persons striving to keep their attention on 

 a difficult subject will resort to movements of various un- 

 meaning kinds, such as pacing the room, drumming with 

 the fingers, playing with keys or watch-chain, scratching 



* I have begun to inquire experimentally whether any of the measurable 

 functions of the workmen change after the din of machinery stops at a 

 workshop. So far I have found no constant results as regards either pulse, 

 breathing, or strength of squeeze by the hand. I hope to prosecute the in- 

 quiry farther (May, 1890). 



