we return so often, that at last even our careless thoughts begin to
run in a scientific channel.

I quite admit that our mental energy is limited in quantity, and I
know that many zealous students try to do more than is good for them.
But the question about the introduction of experimental study is not
entirely one of quantity. It is to a great extent a question of
distribution of energy. Some distributions of energy, we know, are
more useful than others, because they are more available for those
purposes which we desire to accomplish.

Now in the case of study, a great part of our fatigue often arises,
not from those mental efforts by which we obtain the mastery of the
subject, but from those which are spent in recalling our wandering
thoughts; and these efforts of attention would be much less fatiguing
if the disturbing force of mental distraction could be removed.

This is the reason why a man whose soul is in his work always makes
more progress than one whose aim is something not immediately
connected with his occupation. In the latter case the very motive of
which he makes use to stimulate his flagging powers becomes the means
of distracting his mind from the work before him.

There may be some mathematicians who pursue their studies entirely for
their own sake. Most men, however, think that the chief use of
mathematics is found in the interpretation of nature. Now a man who
studies a piece of mathematics in order to understand some natural
phenomenon which he has seen, or to calculate the best arrangement of
some experiment which he means to make, is likely to meet with far
less distraction of mind than if his sole aim had been to sharpen his