But the mind is not satisfied with a moderate course alone: its perceptions must also be sufficiently diversified. Number without variety constitutes not an agreeable train. In comparing a few objects, uniformity is agreeable: but the frequent reiteration of uniform objects becomes unpleasant. One tires of a scene that is not diversified; and soon feels a sort of unnatural restraint when confined within a narrow range, whether occasioned by a retarded succession or by too great uniformity. An excess in variety is, on the other hand, fatiguing. This is even perceptible in a train composed of related objects: much more where the objects are unrelated; for an object, unconnected with the former train, gains not admittance without effort; and this effort, though scarce perceptible in a single instance, becomes by frequent reiteration exceeding painful. Whatever be the cause, the fact is certain, that a man never finds himself more at ease, than when his perceptions succeed each other with a certain degree, not only of velocity, but also of variety. Hence it proceeds, that a train consisting entirely of ideas of memory, is never painful by too great variety; because such ideas are not introduced otherwise than according to their natural connections[96]. The pleasure of a train of ideas, is the most remarkable in a reverie; especially where the imagination interposes, and is active in coining new ideas, which is done with wonderful facility. One must be sensible, that the serenity and ease of the mind in this state, makes a great part of the enjoyment. The case is different where external objects enter into the train; for these, making their appearance without any order, and without any connection save that of contiguity, form a train of perceptions that may be extremely uniform or extremely diversified; which, for opposite reasons, are both of them painful.