able discipline to settle the
business. I have myself often called in the aid of Euclid for a few
moments, and always with good success. A little wholesome schooling of
the mind upon lines and angles and proportions, when it is not in the
right mood for study, will commonly make it quite willing to exchange
them for the labor of composition, as the easier task of the two."

There is sound philosophy perhaps in this recommendation. Many persons
have observed that the preliminary process of "composing the thoughts"
is one which requires a little time and effort, especially where one
comes to his subject from a period of exercise, or repose, or any other
condition in which the brain has not been active. The functional
activity of the brain depends on the copious supply of the arterial
blood, its activity varying with that supply, increasing as that supply
is greater, and relaxing when it is diminished. But unlike other organs
of the body, the brain is densely packed in an unyielding cavity, and
there must be room made for this increased volume of circulation
whenever it takes place. This is accomplished, physiologists tell us, in
the cerebro-spinal fluid, the quantity of which has been estimated at
two ounces. This fluid is readily absorbed and as readily reproduced,
and thus its quantity varies in a certain inverse proportion to the
volume of the circulation of blood in the brain; and by this means an
equality of pressure is secured throughout all the variations in the
force of the circulation. The act of adjustment between this balancing
fluid and the blood requires a little period for its completion, and
therefore the brain cannot instantaneously be brought to its maximum
action.

Hence, where the circulation has been diverted from the brain, and the
proposed mental effort requires it to be vigorously revived in the
brain, time must be allowed for this process of adjustment, and room
must be made for the needed supply of blood; and perhaps a familiar
demonstration in mathematics, which fixes the attention, and will
instantly detect any delinquency of that faculty, may often be one of
the best modes of employing this transition period, and aiding the
change.

We may observe here the singular paradox, which we believe that the
philosophy of the mind and the experience of the scholar equally
establish, that what are usually called the heaviest or severest
subjects of thought are the least exhausting to the thinker. How