The effect of custom with relation to a specific habit, is displayed through all its varieties in the use of tobacco. The taste of this plant is at first extremely unpleasant. Our disgust lessens gradually till it vanish altogether; at which period the plant is neither agreeable nor disagreeable. Continuing the use, we begin to relish it; and our relish increases by use till it come to its utmost extent. From this state it gradually decays, while the habit becomes stronger and stronger, and consequently the pain of want. The result is, that when the habit has acquired its greatest vigor, the pleasure of gratification is gone. And hence it is, that we often smoke and take snuff habitually, without so much as being conscious of the operation. We must except gratification after the pain of want; because gratification in that case is at the height when the habit is strongest. It is of the same kind with the joy one feels upon being delivered from the rack, the cause of which is explained above[31]. This pleasure however is but occasionally the effect of habit; and however exquisite, is guarded against as much as possible, by preventing want. With regard to the pain of want, I can discover no difference betwixt a generic and specific habit: the pain is the same in both. But these habits differ widely with respect to the positive pleasure. I have had occasion to observe, that the pleasure of a specific habit decays gradually till it become imperceptible. Not so the pleasure of a generic habit. So far as I can discover, this pleasure suffers little or no decay after it comes to its height. The variety of gratification preserves it entire. However it may be with other generic habits, the observation I am certain holds with respect to the pleasures of virtue and of knowledge. The pleasure of doing good has such an unbounded scope, and may be so variously gratified, that it can never decay. Science is equally unbounded; and our appetite for knowledge has an ample range of gratification, where discoveries are recommended by novelty, by variety, by utility, or by all of them.