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subtilis. So that that hypothesis, how ingeniously soever explained, by showing, that the parts of sensible bodies are held together by the pressure of other external insensible bodies, reaches not the parts of the æther itself; and by how much the more evident it proves, that the parts of other bodies are held together by the external pressure of the æther, and can have no other conceivable cause of their cohesion and union, by so much the more it leaves us in the dark concerning the cohesion of the parts of the corpuscles of the æther itself; which we can neither conceive without parts, they being bodies, and divisible; nor yet how their parts cohere, they wanting that cause of cohesion, which is given of the cohesion of the parts of all other bodies.
$. 24. But, in truth, the pressure of any ambient fluid, how great soever, can be no intelligible cause of the cohesion of the solid parts of matter.
For though such a pressure may hinder the avulsion of two polished superficies, one from another, in a line perpendicular to them, as in the experiment of two polished marbles; yet it can never, in the least, hinder the separation by a motion, in a line parallel to those surfaces. Because the ambient fluid, having a full liberty to succeed in each point of space, deserted by a lateral motion, resists such a motion of bodies so joined, no more than it would resist the motion of that body, were it on all sides invironed by that fluid, and touched no other body: and therefore, if there were no other cause of cohesion, all parts of bodies must be easily separable by such a lateral sliding motion. For if the pressure of the æther be the adequate cause of cohesion, wherever that cause operates not, there can be no cohesion. And since it cannot operate against such a lateral separation, (as has been shown) therefore in every imaginary plane, intersecting any mass of matter, there could be no more cohesion, than of two polished surfaces, which will always, notwithstanding any imaginable pressure of a fluid, easily slide one from another. So that, perleps, how clear an idea soever we think we have of the extension of body, which is nothing but the cohesion of C4
solid parts, he that shall well consider it in his mind may have reason to conclude, that it is as easy for him to have a clear_idea, how the soul thinks, as how body is extended. For since body is no farther, nor otherwise extended, than by the union and cohesion of its solid parts, we shall very ill comprehend the extension of body, without understanding wherein consists the union and cohesion of its parts; which seems to me as incomprehensible, as the manner of thinking, and how it is performed.
§. 25. I allow it is usual for most people to wonder how any one should find a difficulty in what they think they every day observe. Do we not see, will they be ready to say, the parts of bodies stick firmly together? Is there any thing more common ? And what doubt can there be made of it ? And the like, I say, concerning thinking and voluntary motion : Do we not every moment experiment it in ourselves; and therefore can it be doubted ? The matter of fact is clear, I confess; but when we would a little nearer look into it, and consider how it is done, there I think we are at a loss, both in the one, and the other; and can as little understand how the parts of body cohere, as how we ourselves perceive, or move. I would have any one intelligibly explain to me, how the parts of gold, or brașs, (that but now in fusion were as loose from one another, as the particles of water, or the sands of an hour-glass) come in a few moments to be so united, and adhere so strongly one to another, that the utmost force of men's arms cannot separate them : a considera ing man will, I suppose, be here at a loss, to satisfy his own, or another man's understanding.
§. 26. The little bodies that cainpose that fluid we call water, are so.extremely small, that I have never heard of any one, who by a microscope, (and yet I have heard of some that have magnified to ten ihousand; nay, to much above a hundred thousand times) pretended to perceive their distinct bulk, figure, or mo. tion: and the particles of water are also so perfectly loose one from another, that the least force sensibly separates them. Nay, if we consider their perpetual
motion, motion, we must allow them to have no cohesion one with another; and yet let but a sharp cold come, they unite, they consolidate,' these little atoms cohere, and are not, without great force, separable. He that could find the bonds that tie these heaps of loose little bodies together so firmly ; he that could make known the cement that makes them stick so fast one to another; would discover a great, and yet unknown secret: and yet when that was done, would he be far enough from making the extension of body (which is the cohesion of its solid parts) intelligible, till he could show wherein consisted the union, or consolidation of the parts of those bonds, or of that cement, or of the least particle of matter that exists. Whereby it appears, that this primary and supposed obvious quality of body will be found, when examined, to be as incomprehensible as any thing belonging to our minds, and a solid extended substance as hard to be conceived as a thinking immaterial one, whatever difficulties some would raise against it.
§. 27. For to extend our thoughts a little farther, that pressure, which is brought to explain the cohesion of bodies, is as unintelligible as the cohesion itself
. For if matter be considered, as no doubt it is, finite, let any one send his contemplation to the extremities of the universe, and there see what conceivable hoops, what bond he can imagine to hold this mass of matter in so close a pressure together; from whence steel has its firmness, and the parts of a diamond their hardness and indissolubility. If matter be finite, it must have its extremes; and there must be something to hinder it from scattering asunder. If, to avoid this difficulty, any one will throw himself into the supposition and abyss of infinite matter, let him consider what light he thereby brings to the cohesion of body, and whether he be ever the nearer making it intelligible, by resolving it into a supposition, the most absurd and most incomprehensible of all other : So far is our extension of body (which is nothing but the cohesion of solid parts) from being clearer, or more distinct, when we would inquire into the nature, cause, or manner of it, than the idea of thinking.
§. 28. Another idea we have of body is Communica. tion of mo
the power of communication of inotion by tion by im- impulse; and of our souls, the power of pulse, or by exciting motion by thought. These ideas, thought,
the one of body, the other of our minds, equally in telligible.
every day's experience clearly furnishes us
with: but if here again we inquire how this is done, we are equally in the dark. For to the communication of motion by impulse, wherein as much motion is lost to one body, as is got to the other, which is the ordinariest case, we can have no other conception, but of the passing of motion out of one body into another; which, I think, is as obscure and unconceivable, as how our minds move or stop our bodies by thought; which we every moment find they do. The increase of motion by impulse, which is observed or believed sometimes to happen, is yet harder to be understood. We have by daily experience clear evidence of motion produced both by impulse and by thought; but the manner how, hardly comes within our comprehension; we are equally at a loss in both. So that however we consider motion, and its communication, either from body or spirit, the idea which belongs to spirit is at least as clear as that which belongs to body. And if we consider the active power of moving, or, as I may call it, motivity, it is much clearer in spirit than body ; since two bodies, placed by one another at rest, will never afford us the idea of a power in the one to move the other, but by a borrowed motion : whereas the mind, every day, affords us ideas of an active power of moving of bodies; and therefore it is worth our consideration, whether active power be not the proper attribute of spirits, and passive power of matter. Hence may be conjectured, that created spirits are not totally separate from matter, because they are both active and passive. Pure spirit, viz. God, is only active; pure matter is only passive; those beings that are both active and passive, we may judge to partake of both. But be that as it will, I
think, we have as many, and as clear ideas belonging to spirit, as we have belonging to body, the substance each being equally unknown to us; and the idea of thinking in spirit as clear as of extension in body; and the communication of motion by thought, which we attribute to spirit, is as evident as that by impulse, which we ascribe to body. Constant experience makes us sensible of both these, though our narrow understandings can comprehend neither. For when the mind would look beyond those original ideas we have from sensation or reflection, and penetrate into their causes, and manner of production, we find still it discovers nothing but its own short-sightedness.
$. 29. To conclude; sensation convinces us, that there are solid extended substances; and reflection, that there are thinking ones: experience assures us of the existence of such beings; and that the one hath a power to move body by impulse, the other by thought; this we cannot doubt of. Experience, I say, every moment furnishes us with the clear ideas, both of the one and the other. But beyond these ideas, as received from their proper sources, our faculties will not reach. If we would inquire farther into their nature, causes, and manner, we perceive not the nature of extension clearer than we do of thinking. If we would explain them any farther, one is as easy as the other; and there is no more difficulty to conceive how a substance we know not should by thought set body into motion, than how a substance we know not should by impulse set body into motion. So that we are no more able to discover wherein the ideas belonging to body consist, than those belonging to spirit. From whence it seems probable to me, that the simple ideas we receive from sensation and reflection are the boundaries of our thoughts ; beyond which the mind, whatever efforts it would make, is not able to advance one jot; nor can it make any discoveries, when it would pry into the nature and hidden causes of those ideas.
$. 30. So that in short, the idea we have Idea of body of spirit, compared with the idea we have and spirit of body, stands thus : the substance of spi- compared.