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ing the rays in the fame order as they come from other bodies, fhow us their images.
The rays that are reflected from opake bodies, always bring with them to the eye the idea of colour; and this colour is nothing elfe, in the bodies, but a difpofition to reflect to the eye more copioufly one fort of rays than another. For particular rays are originally endowed with particular colours; fome are red, others blue, others yellow, and others green, &c.
Every ray of light, as it comes from the fun, seems a bundle of all thefe feveral forts of rays; and as some of them are more refrangible than others; that is, are more turned out of their courfe, in paffing from one medium to another; it follows, that after fuch refraction they will be feparated, and their diftinct colour obferved. Of these, the most refrangible are violet, and the least red; and the intermediate ones, in order, are indigo, blue, green, yellow, and orange. This feparation is very entertaining, and will be obferved with pleasure in holding, a prifm in the beams of the fun.
As all thefe rays differ in refrangibility, fo they do in reflexibility; that is, in the property of being more eafily reflected from certain bodies, than from others; and hence arife, as hath been faid, all the colours of bodies; which are, in a manner, infinite, as an infinite number of compofitions and proportions, of the original colours, may be imagined.
The whiteness of the fun's light is compounded of all the original colours, mixed in a due proportion.
Whiteness, in bodies, is but a difpofition to reflect all colours of light, nearly in the proportion they are mixed in the original rays; as, on the contrary, blackness is only a difpofition to abforb or ftifle, without reflection, most of the rays of every fort that fall on the bodies.
Light is fucceffively propagated with an almoft inconceivable swiftnefs; for it comes from the fun, to this our earth, in about feven or eight minutes of time, which distance is about 80,000,000 English miles.
Befides colour, we are fuppofed to fee figure; but, in truth, that which we perceive when we fee figure, as perceiveable by fight, is nothing but the termination of
NEXT to feeing, hearing is the most extenfive of our fenfes. The ear is the organ of hearing, whofe curious ftructure is to be learnt from anatomy.
That which is conveyed into the brain by the ear is called found; 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 found, is a vibration of the air, caufed by an exceeding fhort, but quick, tremulous motion of the body, from which it is propagated; and therefore we coniider and denominate them as bodies founding.
That found is the effect of fuch a fhort, brisk, vibrating motion of bodies, from which it is propagated, may be known from what is obferved and felt in the ftrings of inftruments, and the trembling of bells, as long as we perceive any found come from them; for as foon as that vibration is ftopt, or ceafes in them, the perception ceases alfo.
The propagation of found is very quick, but not approaching that of light. Sounds move about 1140 English feet in a fecond of time; and in feven or eight minutes of time, they move about one hundred English miles.
SMELLING is another fenfe, that seems to be wrought on by bodies at a diftance; though that, which immediately affects the organ, and produces in us the fenfation of any fmell, are effluvia, or invifible particles, that, coming from bodies at a distance, immediately affect tne olfactory nerves.
Smelling bodies fecm perpetually to fend forth effluvia, or steams, without fenfibly wafting at all. a grain of mufk will fend forth odoriferous particles for fcores of years together, without its being fpent; whereby one would conclude that thefe particles are very fmall;
and yet it is plain, that they are much groffer than the rays of light, which have a free paffage through glass; and groffer alfo than the magnetic effluvia, which pafs freely through all bodies, when those that produce smell will not pafs through the thin membranes of a bladder, and many of them fcarce ordinary white paper.
There is a great variety of finells, though we have but a few names for them; fweet, ftinking, four, rank, and mufty, are almost all the denominations we have for odours; though the fmell of a violet, and of musk, both called fweet, are as diftinct as any two smells whatfoever.
TASTE is the next fense to be confidered.
Bodies that emit light, founds, and fmells, 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 tafte it not, how near foever it be.
It may be observed of tastes, that though there be a great variety of them, yet, as in fmells, they have only fome few general names; as fweet, bitter, four, harsh, rank, and fome_few others.
THE fifth and laft of our fenfes is touch; a fenfe fpread over the whole body, though it be moft eminently placed in the ends of the fingers.
By this fenfe the tangible qualities of bodies are difcerned; as hard, foft, fmooth, rough, dry, wet, clammy, and the like.
But the most confiderable of the qualities, that are I perceived by this fenfe, are heat and cold.
The due temperament of those two oppofite qualities, is the great inftrument of nature, that he makes ufe of in moft, if not ail, her productions.
Heat is a very brisk agitation of the infenfible parts of the object, which produces in us that sensation, from whence we denominate the object hot; fo what in our sensation is heat, in the object is nothing but motion. This appears by the way whereby heat is produced; for we fee that the rubbing of a brafs nail upon a board will make it very hot; and the axle-trees of carts and coaches are often hot, and fometimes to a degree, that it fets them on fire, by the rubbing of the nave of the wheel upon it.
On the other fide, the utmost degree of cold is the ceffation of that motion of the infenfible 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; fo that feels hot to one, which feems cold to another; nay, the fame body, felt by the two hands of the fame man, may at the fame time appear hot to the one, and cold to the other; because the motion of the infenfible particles of it may be more brisk than that of the particles of the other.
Befides the objects before-mentioned, which are peculiar to each of our fenfes, as light, and colour of the fight; found of hearing; odours of fmelling; favours of tafting; and tangible qualities 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; fome founds delight, and others grate the car; heat in a certain degree is very pleasant, which may be augmented to the greatest torment; and fo the reft.
Thefe five fenfes are common to beafts with men ; nay, in fome of them, fome brutes exceed mankind. But men are endowed with other faculties, which far excel any thing that is to be found in the other animals in this our globe.
Memory alfo brutes may be fuppofed to have, as well
HE understanding of man does fo furpass 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 confideration of human understanding, and the distinct operations thereof.
The lowest degree of it confifts in perception, which we have before in part taken notice of, in our discourse of the fenfes. Concerning which it may be convenient farther to obferve, that, to conceive a right notion of perception, we must confider the diftinct objects of it, which are fimple ideas; v. g. fuch as are thofe fignified by these words, fcarlet, blue, fweet, bitter, heat, cold, &c. from the other objects of our fenfes; 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 thefe fimple ideas are made, by putting them together, several compounded or complex ideas; as those fignified by the words pebble, marygold, horse.
The next thing the understanding doth in its progress to knowledge, is to abstract its ideas, by which abstraction they are made general.
A general idea is an idea in the mind, confidered there as feparated from time and place; and fo capable to represent any particular being that is conformable to it. Knowledge, which is the highest degree of the fpeculative faculties, confifts in the perception of the truth of affirmative, or negative, propofitions.
This perception is either immediate, or mediate. Im mediate perception of the agreement, or difagreement, of two ideas, is when, by comparing them together in our minds, we fee, or, as it were, behold, their agreement, or difagreement. This therefore is called intuitive knowledge. Thus we fee that red is not green; Ff4