914 The American Naturalist. [October, 
Thus if it is a line that he is to remember, he is shown another line and 
judges the relation of the two. 
These two methods may be used with many variations of detail into 
which we need not enter; it is sufficient to have shown that it is pos- 
sible to make an experimental study of memory. I shall proceed to 
indicate the principal results which have up to the present been reached 
by science. There is, perhaps, no question of more importance to 
pedagogy. As I can only give a bird’s-eye view of the whole, I will 
not mention any name, nor will I enter into the details of any experi- 
ment ; it is sufficient to sum up in a few bare statements the results 
that have been attained. 
1. Partial memories—We know to day that the memory is not a 
unit, but that there exists for each individual a series of partial memo- 
ries which are distinct and independent; that these memories are un- 
equally developed, and that in a certain number of pathological cases 
one of the memories may disappear altogether, leaving the rest intact 
or nearly so. The most striking example of this that can be cited is 
aphasia, a disorder in which the memory and images of words are 
affected in a special manner; the patient usually retains the memory 
and images of objects, and remains in possession of his intellect. Ex- 
amples of the partial development of memory are met with among some 
professional exhibitors, such as chess players and (more especially) 
lightning calculators. j 
2. The measurement of memory.—Although the methods used for 
measuring the memory may have been crude, as they still are, it 1s 
nevertheless a great advance to be able to introduce the concept of 
measurement into this problem at all. So far attempts have been made 
to measure but one kind of memory, the direct faculty of acquisition. 
The experiments deal with the number of memory-images that can be 
stored up at a single trial, without allowing the subject time to rest. 
This is called in English the “ mental span ” of the memory; I have 
proposed for it the term “ faculté de prehension.” Several successive 
investigations have already been made on the measurement of the 
memory for figures and syllables; these are localized memories, the 
development of which cannot be considered as a sign of the develop- 
ment of the other memories; we must, therefore, make many reserva- 
tions in interpreting the conclusions to be drawn from these experi- 
‘ments. The experiment may be made as follows: a series of figures 
is read to the subject at a regular speed (the speed used is in general 
_ two figures per second) and without any special accentuation ; as s000 
as he has heard the series, the subject, having been told beforehand of 
