are naturally difpofed to conceive as fomething which would be abfolutely incompreffible, and which would refift, with unconquerable force, every attempt to reduce it within narrower dimenfions. If the folid and refifting fubftance, without moving out of its place, should admit into the fame place another folid and refifting fubftance, it would from that moment, in our apprehenfion, ceafe to be a folid and refifting fubftance, and would no longer appear to poffefs that quality, by which alone it is made known to us, and which we therefore confider as conftituting its nature and effence, and as altogether infeparable from it. Hence our notion of what has been called impenetrability of matter; or of the abfolute impoffibility that two folid refifting fubftances fhould occupy the fame place at the fame time.

This doctrine, which is as old as Leucippus, Democritus, and Epicurus, was in the laft century revived by Gaffendi, and has fince been adopted by Newton and the far greater part of his followers. It may at prefent be confidered as the established fyftem, or as the fyftem that is most in fashion, and most approved of by the greater part of the philofophers of Europe. Though it has been oppofed by feveral puzzling arguments, drawn from that fpecies of metaphyfics which confounds every thing and explains nothing, it

feems

feems upon the whole to be the most fimple, the most distinct, and the most comprehenfible account that has yet been given of the pho nomena which are meant to be explained by it. I fhall only obferve, that whatever fyftem may be adopted concerning the hardness or foftnefs, the fluidity or folidity, the compreffibility, or incompreffibility of the refifting fubstance, the certainty of our diftinct fenfe and feeling of its Externality, or of its entire independency upon the organ which perceives it, or by which we perceive it, cannot in the fmallest degree be affected by any fuch fyftem, I fhall not therefore attempt to give any further account of fuch fyftems.

Heat and cold being felt by almost every part of the human body, have commonly been ranked along with folidity and resistance, among the qualities which are the objects of Touch. It is not, however, I think, in our language proper to fay that we touch, but that we feel the qualities of heat and cold. The word feeling, though in many cafes we ufe it as fynonimous to touching, has, however, a much more extenfive fignification, and is frequently employed to denote our internal, as well as our external, affections. We feel hunger and thirft, we feel joy and forrow, we feel love and hatred.

Heat and cold, in reality, though they may frequently be perceived by the fame parts of

the human body, conftitute an order of fen fations altogether different from those which are the proper objects of Touch. They are naturally felt, not as preffing upon the organ, but as in the organ. What we feel while we ftand in the funshine during a hot, or in the fhade during a frofty, day, is evidently felt, not as preffing upon the body, but as in the body. It does not neceffarily fuggeft the prefence of any external object, nor could we from thence alone infer the existence of any fuch object. It is a fenfation which neither does nor can exift any where but either in the organ which feels it, or in the unknown principle of perception, whatever that may be, which feels in that organ, or by means of that organ. When we lay our hand upon a table, which is either heated or cooled a good deal beyond the actual temperature of our hand, we have two diftinct perceptions: first, that of the folid or refifting table, which is neceffarily felt as fomething external to, and independent of, the hand which feels it: and fecondly, that of the heat or cold, which by the contact of the table is excited in our hand, and which is naturally felt as nowhere but in our hand, or in the principle of perception which feels in our hand.

But though the fenfations of heat and cold do not neceffarily fuggeft the presence of any external object, we foon learn from experi

ence

ence that they are commonly excited by fome fuch object fometimes by the temperature of fome external body immediately in contact with our own body, and fometimes by fome body at either a moderate or a great distance from us; as by the fire in a chamber, or by the fun in a Summer's day. By the frequency and uniformity of this experience, by the cuftom and habit of thought which that frequency and uniformity neceffarily occafion, the Internal Senfation, and the External Cause of that Senfation, come in our conception to be fo ftrictly connected, that in our ordinary and careless way of thinking, we are apt to confider them as almoft one and the fame thing, and therefore denote them by one and the fame word. The confufion, however, is in this cafe more in the word than in the thought; for in reality we ftill retain fome notion of the diftinction, though we do not always evolve it with that accuracy which a very flight degree of attention might enable us to do. When we move our hand, for example, along the furface of a very hot or of a very cold table, though we fay that the table is hot or cold in every part of it, we never mean that, in any part of it, it feels the fenfations either of heat or of cold, but that in every part of it, it poffeffes the power of exciting one or other of thofe fenfations in our bodies. The philofophers who have taken fo

much

much pains to prove that there is no heat in the fire, meaning that the fenfation or feeling of heat is not in the fire, have laboured to refute an opinion which the most ignorant of mankind never entertained. But the fame word being, in common language, employed to fignify both the fenfation and the power of exciting that fenfation, they, without knowing it perhaps, or intending it, have taken advantage of this ambiguity, and have triumphed in their own fuperiority, when by irresistible arguments they establish an opinion which, in words indeed, is diametrically opposite to the moft obvious judgments of mankind, but which in reality is perfectly agreeable to those judgments.

Of the Senfe of TASTING.

WHEN We taste any folid or liquid fubftance, we have always two diftinct perceptions; first, that of the folid or liquid body, which is naturally felt as preffing upon, and therefore as external to, and independent of, the organ which feels it; and fecondly, that of the particular taste, relish, or favour which it excites in the palate or organ of Tafting, and which is naturally felt, not as preffing upon, as external to, or as independent of, that organ; but as altogether in the organ, and nowhere

but