of that species; an image of the pillar itself.  The pillar immediately succeeding increases it; that which follows renews and enforces the impression; each in its order as it succeeds, repeats impulse after impulse, and stroke after stroke, until the eye, long exercised in one particular way, cannot lose that object immediately, and, being violently roused by this continued agitation, it presents the mind with a grand or sublime conception.  But instead of viewing a rank of uniform pillars, let us suppose that they succeed each other, a round and a square one alternately.  In this case the vibration caused by the first round pillar perishes as soon as it is formed; and one of quite another sort (the square) directly occupies its place; which however it resigns as quickly to the round one; and thus the eye proceeds, alternately, taking up one image, and laying down another, as long as the building continues.  From whence it is obvious that, at the last pillar, the impression is as far from continuing as it was at the very first; because, in fact, the sensory can receive no distinct impression but from the last; and it can never of itself resume a dissimilar impression:  besides every variation of the object is a rest and relaxation to the organs of sight; and these reliefs prevent that powerful emotion so necessary to produce the sublime.  To produce therefore a perfect grandeur in such things as we have been mentioning, there should be a perfect simplicity, an absolute uniformity in disposition, shape, and coloring.  Upon this principle of succession and uniformity it may be asked, why a long bare wall should not be a more sublime object than a colonnade; since the succession is no way interrupted; since the eye meets no check; since nothing more uniform can be conceived?  A long bare wall is certainly not so grand an object as a colonnade of the same length and height.  It is not altogether difficult to account for this difference.  When we look at a naked wall, from the evenness of the object, the eye runs along its whole space, and arrives quickly at its termination; the eye meets nothing which may interrupt its progress; but then it meets nothing which may detain it a proper time to produce a very great and lasting effect.  The view of a bare wall, if it be of a great height and length, is undoubtedly grand; but this is only one idea, and not a repetition of similar ideas:  it is therefore great, not so much upon the principle of infinity, as upon that of vastness.  But we are not so powerfully affected with any one impulse, unless it be one of a prodigious force indeed, as we are with a succession of similar impulses; because the nerves of the sensory do not (if I may use the expression) acquire a habit of repeating the same feeling in such a manner as to continue it longer than its cause is in action; besides, all the effects which I have attributed to expectation and surprise in Sect. 11, can have no place in a bare wall.