A MEASURE OF MENTAL CAPACITY. 761 



ing that give the pupils happy opportunities to loosen the reins of 

 their tired attention and forget the hard present. " One can com- 

 pel children to sit and be still," says Burgerstein, " but he must 

 not mistake ; they will still in many cases take mental rest, or 

 make a change for themselves, and not follow the course of the 

 teaching if they are tired." Hence arises the unexpected conse- 

 quence that, under the present extension of instruction, tedious 

 teachers are a necessity. 



To a certain extent the dangers of mental overwork have been 

 recognized for a long time. All those efforts to introduce phys- 

 ical exercises into the school hours have in view, to a greater or 

 less extent, the defense of the childish brain against the imminent 

 dangers of a one-sided tension by alternating mental and muscu- 

 lar exertion. Gymnastic and movement exercises, manual train- 

 ing, and singing and drawing, to a certain extent, are intended to 

 furnish rest-pauses for recovery from mental weariness and the 

 gradual restoration of the previous efficiency. For this purpose 

 such have been interposed at intervals to relieve the strictly men- 

 tal work. 



The physical exercises are doubtless of considerable value 

 toward the complete building up of the personality, but they 

 must be regarded as relaxations only within certain limits. It is, 

 at any rate, fundamentally false to regard physical effort as in 

 any way a suitable preparation for mental labor. Protracted ex- 

 periments, pursued under my direction, have given the result that 

 a simple walk of from one to two hours diminishes the mental 

 efficiency in adults at least as much as about an hour's work in 

 addition. The same is the case to a more limited extent with 

 much less important bodily efforts. It is well known to pupils 

 and teachers that the greater the interval of active play, the 

 longer time is required for collecting the faculties before return- 

 ing to mental work. From these experiments has arisen the de- 

 mand that physical exercises should not be regarded in the plan 

 of teaching as relaxations ; and the demand for hard mental work 

 should not be imposed on the pupil till after a rest from them. 



By far the most important compensation for all effects of 

 fatigue is sleep. Everybody, even the man mentally most inert, 

 develops when awake a mass of mental effort which he can not 

 afford continuously without suffering. We need, therefore, regu- 

 larly recurring periods in which the consumption of mental force 

 shall be slower than the continuous replacement. The lower the 

 degree to which the activity of the brain sinks, then, the more 

 rapid and more complete the recovery. 



The mental vigor of most men is usually maintained at a cer- 

 tain height for the longest time in the forenoon. The evidences 

 of fatigue come on later at this time of day than in the evening, 



TOL. Xl.IX. 59 



