| The consequence of this is, that it is not from the mere removal of visible objects we receive the impression of extension without matter; and that the idea of utter darkness can never be the same with that of vacuum. |
| Suppose again a man to be Supported in the air, and to be softly conveyed along by some invisible power; it is evident he is sensible of nothing, and never receives the idea of extension, nor indeed any idea, from this invariable motion. |
| Even supposing he moves his limbs to and fro, this cannot convey to him that idea. |
| He feels in that case a certain sensation or impression, the parts of which are successive to each other, and may give him the idea of time: But certainly are not disposed in such a manner, as is necessary to convey the idea of s ace or the idea of space or extension. |
| Since then it appears, that darkness and motion, with the utter removal of every thing visible and tangible, can never give us the idea of extension without matter, or of a vacuum; the next question is, whether they can convey this idea, when mixed with something visible and tangible? |
| It is commonly allowed by philosophers, that all bodies, which discover themselves to the eye, appear as if painted on a plain surface, and that their different degrees of remoteness from ourselves are discovered more by reason than by the senses. |
| When I hold up my hand before me, and spread my fingers, they are separated as perfectly by the blue colour of the firmament, as they coued be by any visible object, which I coued place betwixt them. |
| In order, therefore, to know whether the sight can convey the impression and idea of a vacuum, we must suppose, that amidst an entire darkness, there are luminous bodies presented to us, whose light discovers only these bodies themselves, without giving us any impression of the surrounding objects. |
| We must form a parallel supposition concerning the objects of our feeling. |
| It is not proper to suppose a perfect removal of all tangible objects: we must allow something to be perceived by the feeling; and after an interval and motion of the hand or other organ of sensation, another object of the touch to be met with; and upon leaving that, another; and so on, as often as we please. |
| The question is, whether these intervals do not afford us the idea of extension without body? |
| To begin with the first case; it is evident, that when only two luminous bodies appear to the eye, we can perceive, whether they be conjoined or separate: whether they be separated by a great or small distance; and if this distance varies, we can perceive its increase or diminution, with the motion of the bodies. |
| But as the distance is not in this case any thing coloured or visible, it may be thought that there is here a vacuum or pure extension, not only intelligible to the mind, but obvious to the very senses. |
| This is our natural and most familiar way of thinking; but which we shall learn to correct by a little reflection. |
| We may observe, that when two bodies present themselves, where there was formerly an entire darkness, the only change, that is discoverable, is in the appearance of these two objects, and that all the rest continues to be as before, a perfect negation of light, and of every coloured or visible object. |
| This is not only true of what may be said to be remote from these bodies, but also of the very distance; which is interposed betwixt them; that being nothing but darkness, or the negation of light; without parts, without composition, invariable and indivisible. |
| Now since this distance causes no perception different from what a blind man receives from his eyes, or what is conveyed to us in the darkest night, it must partake of the same properties: And as blindness and darkness afford us no ideas of extension, it is impossible that the dark and undistinguishable distance betwixt two bodies can ever produce that idea. |
| The sole difference betwixt an absolute darkness and the appearance of two or more visible luminous objects consists, as I said, in the objects themselves, and in the manner they affect our senses. |
| The angles, which the rays of light flowing from them, form with each other; the motion that is required in the eye, in its passage from one to the other; and the different parts of the organs, which are affected by them; these produce the only perceptions, from which we can judge of the distance. |
| But as these perceptions are each of them simple and indivisible, they can never give us the idea of extension. |
| We may illustrate this by considering the sense of feeling, and the imaginary distance or interval interposed betwixt tangible or solid objects. |