_Definition._--I understand, by instinct, a law of action, governing and directing the movement of sentient beings--distinct, on the one hand, from the mere blind forces of matter, as attraction, etc., and from reason on the other; a law working to a given end by impulse, yet blindly--the subject not knowing why he thus works; a law innate, inherent in the constitution of the animal, not acquired but transmitted, the origin of which is to be found in the intelligent author of the universe. These I take to be the principal characteristics of that which we term instinct. _Instinct a Law._--It is a _law of action_. In obedience to it the bee constructs her comb, and the ant her chambers, and the bird her nest; and in obedience to it, the animal, of whatever species, seeks that particular kind of food which is intended and provided for it. These are merely instances of the operation of that law. The uniformity and universality which characterize the operations of this principle, show it to be a law of action, and not a merely casual occurrence. _Works by Impulse._--It is a law _working by impulse_, not mechanical or automatic, on the one hand, nor yet rational on the other. The impelling or motive force, in the case supposed, is not that of a weight acting upon machinery, or any like mechanical principle, nor yet the reflex action of a nerve when irritated, or the spasmodic action of a muscle. It is not analogous to the influence of gravitation on the purely passive forms of matter. Nor yet is it that higher principle which we term reason in man. The bird constructs her nest as she does, and the bee her cell, in obedience to some blind yet powerful and unfailing _impulse_ of her nature, guiding and directing her movements, prompting to action, and to this specific form of action, with a restless yearning, unsatisfied until the end is accomplished. Yet the creature does not herself understand the law by which she works. The bee does not know that she constructs her comb at that precise angle which will afford the greatest content in the least space, does not know why she constructs it at that precise angle, could give no reason for her procedure, even were she capable of understanding our question. It is not with her a matter of reflection, nor of reason, at all, but merely of blind, unthinking, yet unerring impulse.