Force is of two kinds; one quiescent, and one exerted by motion. The former, dead weight for example, must be laid aside; for a body at rest is not by that circumstance either agreeable or disagreeable. Moving force only belongs to the present subject; and though it is not separable from motion, yet by the power of abstraction, either of them may be considered independent of the other. Both of them are agreeable, because both of them include activity. It is agreeable to see a thing move: to see it moved, as when it is dragged or pushed along, is neither agreeable nor disagreeable, more than when at rest. It is agreeable to see a thing exert force; but it makes not the thing either agreeable or disagreeable, to see force exerted upon it. Though motion and force are each of them agreeable, the impressions they make are different. This difference, clearly felt, is not easily described. All we can say is, that the emotion raised by a moving body, resembles its cause: it feels as if the mind were carried along. The emotion raised by force exerted, resembles also its cause: it feels as if force were exerted within the mind. To illustrate this difference, I give the following examples. It has been explained why smoke ascending in a calm day, suppose from a cottage in a wood, is an agreeable object[71]. Landscape-painters are fond of this object, and introduce it upon all occasions. As the ascent is natural and without effort, it is delightful in a calm state of mind. It makes an impression of the same sort with that of a gently-flowing river, but more agreeable, because ascent is more to our taste than descent. A fire-work or a _jet d’eau_ rouses the mind more; because the beauty of force visibly exerted, is superadded to that of upward motion. To a man reclining indolently upon a bank of flowers, ascending smoke in a still morning is delightful. But a fire-work or a _jet d’eau_ rouses him from this supine posture, and puts him in motion. A _jet d’eau_ makes an impression distinguishable from that of a water-fall. Downward motion being natural and without effort, tends rather to quiet the mind than to rouse it. Upward motion, on the contrary, overcoming the resistance of gravity, makes an impression of a great effort, and thereby rouses and enlivens the mind. The public games of the Greeks and Romans, which gave so much entertainment to the spectators, consisted chiefly in exerting force, wrestling, leaping, throwing great stones, and such like trials of strength. When great force is exerted, the effort felt within the mind produces great life and vivacity. The effort may be such, as in some measure to overpower the mind. Thus the explosion of gun-powder, the violence of a torrent, the weight of a mountain, and the crush of an earthquake, create astonishment rather than pleasure.