It is a general law of our internal, as well as of our external perceptions, that we distinguish most readily what is least complicated. In a chorus of many voices, a single discordant voice may escape even a nice discriminator of musical sounds, who would have detected instantly the slightest deviation from the melody of a simple air. A juggler, when he wishes to withdraw a single card, is careful to present to us many; and, though the card which he withdraws is truly before our eyes at the very moment at which he separates it from the pack, we do not discover the quick motion which separates it, however suspiciously watchful we may be, because our vigilance of attention is distracted by the number of cards which he suffers to remain. It is not because the card which he removes is not before us, then, that we do not observe the removal of it, but because it is only one of many that are before us. It is precisely the same in those complicated material processes, with which some theorists encumber the simple phenomena of the mind. The difficulty which seems, to them, to attend any diversity whatever in a substance that is identical, simple, indivisible, and incapable of addition or subtraction, remains, indeed, ultimately in all its force, and would strike us equally, if this supposed difficulty were to be considered alone. But many hypothetical vibrations, or other motions, are given to our consideration at the same moment, that glance upon our mental view like the rapid movements of the juggler's hand. We, therefore, do not feel so painfully as before a difficulty which occupies our attention only in part; and, in our feeble estimation of things, to render a difficulty less visible to us, is almost like a diminution of the difficulty itself.