When the mind is set in motion, it requires a stronger exertion to confine its movements within prescribed limits than when it is steadily fixed on one given point.  For instance, it would be easier to meditate on the subject of patriotism, bringing before the mind every quality of the heart and head that this virtue would have a tendency to develop, than to take in, at one comprehensive glance,[76] the different qualities of those several individuals who have been most remarked for the virtue.  Unless the thoughts were under strong and habitual control, they would infallibly wander to other peculiarities of these same individuals, unconnected with the given subject, to curious facts in their lives, to contemporary characters, &c.; thus loitering by the way-side in amusing, but here unprofitable reflection:  for every exercise of thought like that which I have described is only valuable in proportion to the degree of accuracy with which we can contemplate with one instantaneous glance, laid out upon a map as it were, those features only belonging to the given subject, and keeping out of view all foreign ones.  There is perhaps no faculty of the mind more susceptible of evident, as it were tangible, improvement than this:  besides, the exercise of mind which it procures us is one of the highest intellectual pleasures; you should therefore immediately and perseveringly devote your efforts and attention to seek out the best mode of cultivating it.  Even the reading of books which require deep and continuous thought is only a preparation for this higher exercise of the faculties—­a useful, indeed a necessary preparation, because it promotes the habit of fixing the attention and concentrating the powers of the mind on any given point.  In assimilating the thoughts of others, however, with your own mind and memory, the mind itself remains nearly passive; it is as the wax that receives the impression, and must for this purpose be in a suitable state of impressibility.  In exact proportion to the suitableness of this state are the clearness and the beauty of the impression; but even when most true and most deep, its value is extrinsic and foreign:  it is only when the mind begins to act for itself and weaves out of its own materials a new and native manufacture, that the real intellectual existence can be said to commence.  While, therefore, I repeat my advice to you, to devote some portion of every day to such reading as will require the strongest exertion of your powers of thought, I wish, at the same time, to remind you that even this, the highest species of reading, is only to be considered as a means to an end:  though productive of higher and nobler enjoyments than the unintellectual can conceive, it is nothing more than the stepping-stone to the genuine pleasures of pure intellect, to the ennobling sensation of directing, controlling, and making the most elevated use of the powers of an immortal mind.