510 Wisconsin Academy of Sciences, Arts, and Letters. 
large groups of normal children by methods devised expressly 
for this purpose., In the other studies on memory no attempt 
whatever was made to ascertain the comparative strength of 
memory or the rate of growth of memory power for the various 
ages represented in the school period. 
Method. The nine significant digits were grouped in series 
of various lengths ranging from four to nine figures each. An 
effort was made to avoid as far as possible all previously estab¬ 
lished associations in arranging the digits for these series, and 
a sufficient number of series was prepared to avoid repeating 
any series with the same pupil. 
All of the tests were made on a single child at a time; and 
no visitors, listeners, or lookers on were permitted to be present 
at any time. In this particular my study differs from the others 
thus far reported in which all of the pupils of a room wefe 
tested at the same time. Series; of numbers were read to each 
child in a pleasant, agreeable, but firm, and business-like tone 
of voice, and at a rate that seemed to suit each child best, a 
metronome being used to keep the rate absolutely uniform 
after it had once been established for each child. I may say 
that the rate did not vary widely as a general rule and yet there 
were some marked deviations from the'rate used in the room- 
tests made by Prof. Smedley. Children show their individ¬ 
uality in this as well as in all other matters. 
Short series were used at first, so as to' keep clearly within the 
memory span of the child and thus serve to call his attention 
to his own power to reproduce numbers; in this way the child 
was encouraged to do his very best in the subsequent longer 
series which were gradually introduced. Five series of a set 
of given length were read in succession and then the next! longer 
was used in the same way and this was continued until a set 
was reached which the child was unable to reproduce accurately, 
i. e., in five successful trials—making no error in the figures 
nor in their order. The longest series; that a, child could repro¬ 
duce correctly in five consecutive tests was taken as his memory 
span. In many cases a longer series was occasionally correctly 
repeated, but in every case the next shorter series was regarded 
as his limit unless on a subsequent day he reproduced the longer 
series correctly five times in succession. 
Each child was tested on two different days and in some cases 
a third and even a fourth test was made. An effort was made 
