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Proceedings of the Royal Society of Edinburgh. [Sess. 
day. Thus, the increase on the third day is stated as the percentage 
increase over the total output on the second day.” 
The Normal Mental Work Curve. 
The normal mental work curve throughout the fifteen minutes varied 
somewhat in its details in different persons, but certain characteristics 
were common to all. In the various charts, the initial spurt is seen 
to be well marked. It varied from 3 to 25 per cent, above the average 
working capacity. The maximum working capacity was attained in the 
initial spurt in all but Case E, in whom it occurred in the eleventh 
minute. The maximum, other than the initial spurt, was very variable. 
In I it occurred in the third minute, in A and D in the fourth minute, 
in C in the tenth minute, in E and F in the fourteenth, and in B in the 
fifteenth. 
Curve I. — Average Curve of the Seven Normal Persons. 
Showing percentage variation from minute to minute from the average rate 
of the test. 
no — — no 
The curve of the average course of the working capacity in seven 
normal people over five da}AS shows several essentially characteristic 
points. This normal work curve (Curve I.) is probably fairly representative 
of the normal average course of work {vide p. 77). The most striking 
feature of the curve is the extent of the initial spurt. After the fourth 
minute in the interval between the fourth and the fourteenth, the amount of 
work was without exception less than the average. The initial spurt had 
a steep slope from the first minute, and rapidly sank till at the end of the 
second minute, as it approached the line of average, its downward progress 
slowed for the third and fourth minutes, and then abruptly continued 
until the end of the sixth minute. A tendency to spurt was evident in 
the fourteenth minute ; but in the interval between these two spurts the 
rate was not constant. Similar moods do not recur at the same moment 
in successive days. The inconstancy was, however, somewhat regular. It 
consisted of two crests situated between three depressions. The duration 
of the first of these waves was three minutes, and of the second four. It 
