It is the mind only in its fulness which can brood over thoughts till the incubation produces vitality.

Such is the feeling in this act of study.

In Plutarch's time they showed a subterraneous place of study built by Demosthenes, and where he often continued for two or three months together.

Malebranche, Hobbes, Corneille, and others, darkened their apartment when they wrote, to concentrate their thoughts, as Milton says of the mind, "in the spacious circuits of her musing." It is in proportion as we can suspend the exercise of all our other senses that the liveliness of our conception increases--this is the observation of the most elegant metaphysician of our times; and when Lord Chesterfield advised that his pupil--whose attention wandered on every passing object, which unfitted him for study -- should be instructed in a darkened apartment, he was aware of this principle; the boy would learn, and retain what he learned, ten times as well.

We close our eyes whenever we would collect our mind together, or trace more distinctly an object which seems to have faded away in our recollection.