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Light is successively propagated with an almost inconceivable swiftness! for it comes from the sun, to this our earth, in about seven or eight minutes of time, which distance is about 80,000,000 English miles.

Besides colour, we are supposed to see figure; but, in truth, that which we perceive when we see figure, as perceivable by sight, is nothing but the termination of colour.

OF HEARING.

NEXT to seeing, hearing is the most extensive of our senses. The ear is the organ of hearing, whose curious structure is to be learnt from anatomy:

That which is conveyed into the brain by the air is called sound; though, in truth, till it come to reach and affect the perceptive part, it be nothing but motion. The motion, which produces in us the perception of sound, is a vibration of the air, caused by an exceeding short, but quick, tremulous motion of the body, from which it is propagated; and therefore we consider and denomi nate them as bodies sounding.

That sound is the effect of such a short, brisk, and vibrating motion of bodies, from which it is propagated, may be known from what is observed and felt in the strings of instruments, and the trembling of bells, as long as we perceive any sound come from them; for as soon as that vibration is stopt, or ceases in them, the perception ceases also.

The propagation of sound is very quick, but not approaching that of light. Sounds move about 1140 English feet in a second of time; and in seven or eight minutes of time, they move about one hundred English miles.

OF SMELLING.

SMELLING is another sense, that seem to be wrought on by bodies at a distance; though that, which immediately affects the organ and produces in us the sensation of any smell, are effluvia, or invisible particles coming from bodies at a distance, immediately affect the olfactory nerves.

Smelling bodies seem perpetually to send forth effluvia, or steams, without sensibly wasting at all. Thus a grain of musk will send forth odoriferous particles for scores of years together, without its being spent; whereby one would conclude that these particles are very small; and yet it is plain, that they are much grosser than the rays of light, which have a free passage through glass; and. and grosser also than the magnetic effluvia, which pass freely through all bodies, when those that produce smell will not pass through the thin membranes of a bladder, and many of them scarce ordinary white paper.

There is a great variety of smells, though we have but a few names for them; sweet, stinking, sour, rank, and musty, are almost all the denominations we have for odours; though the smell of a violet, and of musk, both called sweet, are as distinct as any two smells whatsoever.

OF TASTE.

TASTE is the next sense to be considered. The organ of taste is the tongue and palate. Bodies that emit light, sounds, and smells, are seen, heard, and smelt at a distance; but bodies are not tasted, but by immediate application to the organ; for till our meat touch our tongues, or palates, we taste it not, how near soever it be.

It may be observed of tastes, that though there be a great variety of them, yet, as in smells, they have only some few general names; as sweet, bitter, sour, harsh, rank, and some few others.

OF TOUCH.

THE fifth and last of our senses is touch; a sense spread over the whole body, though it be most eminently placed in the ends of the fingers.

By this sense the tangible qualities of bodies are discerned; as hard, soft, smooth, rough, dry, wet, clammy, and the like.

But the most considerable of the qualities, that are perceived by this sense, are heat and cold.

The due temperament of those two opposite qualities, is the great instrument of nature, that she makes use of in most, if not all, her productions.

Heat is a very brisk agitation of the insensible parts of the object, which produces in us that sensation, from whence we denominate the object

hot; so what in our sensation is heat, in the object is nothing but motion. This appears by the way whereby heat is produced; for we see that the rubbing of a brass nail upon a board will make it very hot, and the axle-trees of carts and coaches are often hot, and sometimes to a degree that it sets them on fire, by the rubbing of the nave of the wheel upon it.

On the other side, the utmost degree of cold is the cessation of that motion of the insensible particles which to our touch is heat.

Bodies are denominated hot and cold in proportion to the present temperament of that part of our body to which they are applied; so that feels hot to one, which seems cold to another; nay, the same body, felt by the two hands of the same man, may at the same time appear hot to the one, and cold to the other: because the motion of the insensible particles of it may be more brisk than that of the particles of the other.

Besides the objects before-mentioned, which are peculiar to each of our senses, as light, and colour of the sight; sound of hearing; odours of smelling; savours of tasting; and tangible quali ties of the touch: there are two others that are common to all the senses, and those are pleasure and pain, which they may receive by and with their peculiar objects. Thus, too much light offends the eye; some sounds delight, and others grate the ear; heat in a certain degree is very pleasant, which may be augmented to the greatest torment; and so the rest.

These five senses are common to beasts with men; nay, in some of them, some brutes exceed mankind. But men are endowed with other fa

culties, which far excel any thing that is to be found in the other animals of this our globe. Memory also brutes may be supposed to have, as well as men.

CHAP. XII.

OF THE UNDERSTANDING OF MAN.

THE understanding of man does so surpass that of brutes, that some are of opinion brutes are mere machines, without any manner of perception at all. But letting this opinion alone, as ill-grounded, we will proceed to the consideration of human understanding, and the distinct operations thereof.

The lowest degree of it consists in perception, which we have before in part taken notice of, in our discourse of the senses. Concerning which it may be convenient farther to observe, that, to conceive a right notion of perception, we must consider the distinct objects of it, which are simple ideas; v. g. such are those signified by these words, scarlet, blue, sweet, bitter, heat, cold, &c. from the other objects of our senses, to which we may add the internal operations of our minds, as the objects of our own reflection, such as are thinking, willing, &c.

Out of these simple ideas are made, by putting them together, several compounded or complex ideas, as those signified by the words pebble, marygold, horse.

The next thing the understanding doth in its

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