That the various species of _uneasiness_, which are elementary parts of our appetites, recur, at intervals, in which there is some degree of regularity, does not alter their nature, when they _do_ recur, so as to render a peculiar arrangement necessary for including them. The mental states, which constitute the uneasiness that is felt, recur thus at intervals, not from any thing peculiar in the mind itself, the phenomena of which alone we are considering, but because the body is only at intervals in the state, which precedes or induces those peculiar mental affections. If, instead of the _two_ or _three_ periods, at which the appetite of hunger recurs, the nervous system were, one hundred times in the day, at intervals the most irregular, in that state, which is immediately followed by the feeling of hunger, the painful feeling,--and the consequent desire of food, which has been found to relieve it,--would of course, be felt one hundred times in the day. The regularity, therefore, of the recurrence of this state of the nerves, is a phenomenon, which belongs to the consideration of the physiologist of the _body_, not of the physiologist of the _mind_, whose immediate office is finished, when he can trace any particular feeling of the mind to some affection of our organic frame, as its invariable antecedent; and who knowing, therefore, that the feeling of pain in any of our appetites, is the effect or result of some organic affection, is not surprised that it should not recur, when that organic affection has not previously taken place,--any more than he is surprised that we do not enjoy the fragrance of roses or violets, when there are no particles of odour to be inhaled by us; or do not listen to songs and choral harmonies, when there is no vibration to be transmitted to the auditory nerve. It is at certain regular periods, that the full light of day, and the twilight of morning and evening, are perceived by us. But we do not think it necessary, on this account, to give any peculiar name to these visual perceptions, to distinguish them from others less regular, because we know, that the reason of the _periodic_ recurrence of these perceptions, is that the various degrees of sunshine, which produce them, exist only at such intervals. We are _hungry_, when the nerves of the stomach are in a certain state; we perceive the sun, when the organ of vision is in a certain state. It is as little wonderful, that we should _not_ have the feeling of hunger, except when the nerves of the stomach are in this state, as that we should _not_ have the perception of the meridian sun, when the sun itself is beneath our horizon.