The Discovery Of The Child

172 THE DISCOVERY OF THE CHILD

Still plainer is the error in another inset apparently the same
as the one described; that, however, when carefully noticed, differs
from it to some extent. The cylinders are all of the same height,
but the circular sections differ gradually from the first to the last;
from the smallest to that of largest section. That is, there are
narrower and wider cylinders instead of shorter and longer, as
-were those of the first set. If, handled by the knob which is used
to replace them,, a cylinder is replaced in a hole too wide for it,
the error may for the first moment pass unnoticed and by con-
tinuing to inset cylinders narrower than the space needed, there
may persist for a long time the illusion that all is going well. But,
in the end, there will be left one cylinder for which no place is big
-enough, one object out of all left outside the stand.

Here the mistake is so glaring that it at once destroys the
illusion so long cherished. Attention is directed to an evident
problem. All the wrongly placed cylinders must be taken out
.again and each one put back into its own hole.

We come to another inset of the same kind. Here, the cylin-
ders are graduated according to all the dimensions. Not only are
the circular sections diminished gradually as in the second insets,
but the heights also decrease from the tallest cylinder to the short-
-est; the cylinders are thus krger and smaller, keeping the same
form with different dimensions. With this inset also, which presents
'the material control of error, there is repeated a similar exercise.
The four insets, at first sight indistinguishable one from the
other, present to the child who uses them their minute differences,
.and all four by degrees rouse more and more interest, as use reveals
them. There follows as a consequence repetition of the exercise,
which increases the power of the eye for distinguishing things,
:makes more acute the faculty of observation, regulates and guides
•the attention thus trained systematically, stimulates the reasoning
power by applying itself to error and its correction, and if one
may say so, by laying hold of the mental personality .of the child
tfhrougb the senses, furnishes him with constant and far-reaching
^exercise,