79 
1911-12.] A Method of Measuring Mental Processes. 
The tendency to a gradual diminution of the improvement, that is, to 
the attainment and maintenance of a maximum working capacity, was 
still better seen in the course of a second five days of the test (Table II.) 
undertaken by A and B, in which the variation between the first and 
the fifth day was only 8*9 per cent, in A and 5 4 per cent, in B. Although 
Mr A in the initial test had recorded 610, the lowest number of all the 
test persons, on the tenth day he reached 1234 units. Mr B, who in the 
first experiment recorded the highest total — 850, — on the tenth yielded 
1282. In this elementary task, therefore, the rate of improvability 
progressively diminishes : and an approximately uniform standard of 
production seems to be attainable in normal people in spite of any initial 
discrepancy in the mental working capacity. 
Table II. — Showing Output and Percentage Variation in the Second Five 
Days’ Test for A and B (i.e. G and H in Tables). 
Output of A on 6th day .... 1151 
Output of A on 10th day .... 1234 
Output of B on 6th day .... 1200 
Output of B on 10th day .... 1282 
A (G in Tables). 
B (II in Tables). 
Days. 
Percentage Varia- 
tion from Day 
to Day. 
Percentage Varia- 
tion between First 
and Subsequent 
Days. 
Days. 
Percentage Varia- 
tion from Day 
to Day. 
Percentage Varia- 
tion between First 
and Subsequent 
Days. 
7 
- 1-7 
-1*7 
7 
+ 1*4 
+ D4 
8 
+ 2T 
+ 0-3 
8 
+ 09 
+ 2-3 
9 
+ 7-3 
+ 7-7 
9 
+ 5*8 
+ 8-3 
10 
1 
-0-4 
+ 7*2 
10 
- 1-3 
+ 6-8 
As each unit of mental work has a constant difficulty, and as the time 
occupied in the task is essentially that required for the association pro- 
cesses involved (3), the time spent upon each single unit of work can be 
readily calculated, and its abbreviation as a result of exercise and 
habituation ” reckoned. 
Daily Variation. 
The percentage variation from day to day was markedly greatest 
between the first and second days; in no case did the variation on a 
subsequent day exceed that between the first and second. Table I. 
shows the percentage increase per day in the normal persons. Each 
increase is calculated from the total of the work produced on the previous 
