If again, by the maxim, Ars longa, vita brevis, it is intended to signify, that we cannot in any art arrive at perfection; that in reality all the progress we can make is insignificant; and that, as St. Paul says, we must "not count ourselves to have already attained; but that, forgetting the things that are behind, it becomes us to press forward to the prize of our calling,"--this also is true. But this is only ascribable to the limitation of our faculties, and that even the shadow of perfection which man is capable to reach, can only be attained by the labour of successive generations. The cause does not lie in the shortness of human life, unless we would include in its protracted duration the privilege of being for ever young; to which we ought perhaps to add, that our activity should never be exhausted, the freshness of our minds never abate, and our faculties for ever retain the same degree of tenacity and vigour, as they had in the morning of life, when every thing was new, when all that allured or delighted us was seen accompanied with charms inexpressible, and, as Dryden expresses it(10), "the first sprightly running" of the wine of life afforded a zest never after to be hoped for. (10) Aurengzebe. I return then to the consideration of the alleged shortness of life. I mentioned in the beginning of this Essay, that "human life consists of years, months and days; each day containing twenty-four hours." But, when I said this, I by no means carried on the division so far as it might be carried. It has been calculated that the human mind is capable of being impressed with three hundred and twenty sensations in a second of time.(11) (11) See Watson on Time, Chapter II. "How infinitely rapid is the succession of thought! While I am speaking, perhaps no two ideas are in my mind at the same time, and yet with what facility do I slide from one to another! If my discourse be argumentative, how often do I pass in review the topics of which it consists, before I utter them; and, even while I am speaking, continue the review at intervals, without producing any pause in my discourse! How many other sensations are experienced by me during this period, without so much as interrupting, that is, without materially diverting, the train of my ideas! My eye successively remarks a thousand objects that present themselves. My mind wanders to the different parts of my body, and receives a sensation from the chair on which I sit, or the table on which I lean. It reverts to a variety of things that occurred in the course of the morning, in the course of yesterday, the most remote from, the most unconnected with, the subject that might seem wholly to engross me. I see the window, the opening of a door, the snuffing of a candle. When these most perceptibly occur, my mind passes from one to the other, without feeling the minutest obstacle, or being in any degree distracted by their multiplicity(12)." (12) Political Justice, Book IV, Chapter ix.