the other; the same water will, at the same time, seem both hot and cold, according to the disposition of the different organs.  A small degree of any quality, succeeding a greater, produces the same sensation, as if less than it really is, and even sometimes as the opposite quality.  Any gentle pain, that follows a violent one, seems as nothing, or rather becomes a pleasure; as on the other hand a violent pain, succeeding a gentle one, is doubly grievous and uneasy.

This no one can doubt of with regard to our passions and sensations.  But there may arise some difficulty with regard to our ideas and objects.  When an object augments or diminishes to the eye or imagination from a comparison with others, the image and idea of the object are still the same, and are equally extended in the retina, and in the brain or organ of perception.  The eyes refract the rays of light, and the optic nerves convey the images to the brain in the very same manner, whether a great or small object has preceded; nor does even the imagination alter the dimensions of its object on account of a comparison with others.  The question then is, how from the same impression and the same idea we can form such different judgments concerning the same object, and at one time admire its bulk, and at another despise its littleness.  This variation in our judgments must certainly proceed from a variation in some perception; but as the variation lies not in the immediate impression or idea of the object, it must lie in some other impression, that accompanies it.

In order to explain this matter, I shall just touch upon two principles, one of which shall be more fully explained in the progress of this treatise; the other has been already accounted for.  I believe it may safely be established for a general maxim, that no object is presented to the senses, nor image formed in the fancy, but what is accompanyed with some emotion or movement of spirits proportioned to it; and however custom may make us insensible of this sensation and cause us to confound it with the object or idea, it will be easy, by careful and exact experiments, to separate and distinguish them.  For to instance only in the cases of extension and number; it is evident, that any very bulky object, such as the ocean, an extended plain, a vast chain of mountains, a wide forest:  or any very numerous collection of objects, such as an army, a fleet, a crowd, excite in the mind a sensible emotion; and that the admiration, which arises on the appearance of such objects, is one of the most lively pleasures, which human nature is capable of enjoying.  Now as this admiration encreases or diminishes by the encrease or diminution of the objects, we may conclude, according to our foregoing [Book I. Part iii.  Sect. 15.] principles, that it is a compound effect, proceeding from the conjunction of the several effects, which arise from each part of the cause.  Every part, then, of extension, and every unite of number has a separate emotion attending