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any particular forms of substances, either here or elsewhere; but all particular forms of substances, together with our ideas of them, were derived from the general ideas of the intellectual world; so that a triangle was not a triangle, a square not a square, nor a circle a circle, because it had a particular material form, or relative dimensions; but because it partook, in a certain degree, of the qualities of the immutable idea of triangularity, squareness, or rotundity eternally exifting in the divine mind *.
10. When men once renounce the evidence of their senses, either in believing or doubting, there is nothing which they may not believe or doubt with perfect consistency. If we can once persuade ourselves that, because, ideas have no resemblance to their material objects, they may have arisen in the mind without them, we may certainly believe or disbelieve the existence of those material objects, as we please: for our feelings and perceptions are certainly internal; nor can we at all tell how they are connected with any thing external; the mode of conveyance, between the organs of sense and those of perception, being beyond the reach of human discovery. That there is some mode of conveyance the constant recurrence
See Phædon, et de Republicâ, lib, x.
of particular associations proves to the satis-> faction of ordinary men: but if learned philosophers choose to doubt it, because it is not demonstrable, they must doubt on. Scepticism has never attempted to make proselytes by fire or sword, and is therefore at least an innocent absurdity compared with its antagonist bigotry.
11. All its wandering clouds of confusion and perplexity seem to have arisen from employing the Greek word idea, sometimes in its proper sense to signify a mental image or vision, and sometimes in others the most adverse and remote, to signify perception, remembrance, notion, knowledge, and almost every other operation, or result of operation, of which mind is capable. Of motion, for instance, in a particular object, we have a perception when we see or feel it move, and a remembrance afterwards: but of the motion of the earth, either on its axis or in its orbit, we have neither perception nor remembrance, but only a notion, acquired by comparative deductions from other perceptions: while of motion in general we have no particular perception, remembrance or notion; but only general knowledge collected and abstracted from all. Of neither, however, have we any idea, if by idea be meant mental image or resemblance: but, nevertheless, to infer from
thence that we have no adequate perception, remembrance, notion, or knowledge either of motion or body, seems as adverse to sound philosophy as to common sense; there being no more reason why a notion should resemble a perception; a perception, a sensation, or a sensation its object, than that an exertion should resemble an arm; an arm, a lever; or a lever, a weight; nor is it less absurd to make the want of resemblance between the cause, the means, and the end, a ground for doubting the reality of either, in the one case, than in the other *. I could therefore wish to drop or modify the use of the word idea: but it has become too general and established for an individual to attempt it; and I have only to intreat the reader to keep these distinctions in his mind, and apply them occasionally.
12. Among the pleasures of sense, more particularly among those belonging to touch, there is a certain class, which, though arising from negative causes, are nevertheless real and positive pleasures: as when we gradually sink from any violent or excessive degree of action or irritation into a state of tranquillity and re
Since the above was written, a very able and eloquent advocate of the ideal system has appeared in the Right Hon. W. Drummond, whose "Academical Questions" I have read with much delight and instruction, if not with conviction.
tinctly heard, if spoken to one end of a bar of metal or glass, while the other is held between the teeth of the person addressed: but if the disease extends to the auditory nerves; so as to deprive them of their irritability, nothing can be heard by these or any other means. The sound, therefore, appears, in this instance, to be conveyed to those nerves, which communicate with the brain, by means of vibrations received by one solid and elastic substance from another; and thus continued through the bar, the teeth, and the jaw bones.
3. Many of these solid bodies, which are so susceptible of the vibrations of sound, such as glass, and different kinds of metal, are impenetrable to air: wherefore I suspect that sound is produced by some finer fluid mixed with air; and pervading elastic, as light does transparent bodies. Of this fluid, however, if such there be, we can never obtain any adequate knowledge: for, as it is only perceived, as the vehicle of impressions to one sense, our ideas of it must always remain in nearly the same state as those which a man born blind can form of the light of the sun by feeling its warmth. That hard and solid substances should transmit this light, which is excluded by the most soft and porous, is equally unaccountable, as that they should transmit sound. In both, probably, there is a peculiar distribu
tion of the component particles, respectively adapted to the admission of a particular fluid, and of that only.
4. But whatever be the nature of the substance, which produces sound, the sensations, caused by its vibrations upon the organs of hearing, will depend upon the same principles, as those produced by other substances on other organs. Certain modes and degrees of irritation will be pleasant, others painful, and others insipid; and these will vary in different individuals according to the different degrees of sensibility in their respective organs. In some sorts of dogs, this sensibility is 30 exquisite, that the sound of a fife or other very shrill instrument, though perfectly in harmony, gives them very acute pain, when near to their ears; as they testify by loud howlings and complainings. The filing of a saw, or other harsh and discordant sound of that kind, though not loud, will create a very uneasy and even painful sensation in the human organs, which we commonly call setting the teeth on edge; and it seems to be produced by extending the vibrations from the ears to the teeth, instead of from the teeth to the ears: as in the experiment of the metal or glass bar before cited. Extremely loud and jarring sounds, such as those of kettle-drums or artillery, will extend this vibration through the whole body; as I