Convex speculums have the same effect wth concave gla.s.ses.
Qu. Whether concave speculums have the same effect wth convex gla.s.ses?
The reason why convex speculums diminish & concave magnify not yet fully a.s.sign"d by any writer I know.
Qu. Why not objects seen confus"d when that they seem inverted through a convex lens?
Qu. How to make a gla.s.s or speculum which shall magnify or diminish by altering the distance without altering the angle?
No ident.i.ty (other than perfect likeness) in any individuals besides persons(226).
(M386) As well make tastes, smells, fear, shame, wit, virtue, vice, & all thoughts move wth local motion as immaterial spirit.
On account of my doctrine, the ident.i.ty of finite substances must consist in something else than continued existence, or relation to determined time & place of beginning to exist-the existence of our thoughts (which being combined make all substances) being frequently interrupted, & they having divers beginnings & endings.
(M387) Qu. Whether ident.i.ty of person consists not in the Will?
No necessary connexion between great or little optique angles and great or little extension.
Distance is not perceived: optique angles are not perceived. How then is extension perceiv"d by sight?
Apparent magnitude of a line is not simply as the optique angle, but directly as the optique angle, & reciprocally as the confusion, &c. (i.e.
the other sensations, or want of sensation, that attend near vision).
Hence great mistakes in a.s.signing the magnifying power of gla.s.ses. Vid.
Moly[neux], p. 182.
Gla.s.ses or speculums may perhaps magnify or lessen without altering the optique angle, but to no purpose.
Qu. Whether purblind would think objects so much diminished by a convex speculum as another?
Qu. Wherein consists ident.i.ty of person? Not in actual consciousness; for then I"m not the same person I was this day twelvemonth but while I think of wt I then did. Not in potential; for then all persons may be the same, for ought we know.
Mem. Story of Mr. Deering"s aunt.
Two sorts of potential consciousness-natural & praeternatural. In the last -- but one, I mean the latter.
If by magnitude be meant the proportion anything bears to a determined tangible extension, as inch, foot, &c., this, "tis plain, cannot be properly & _per se_ perceived by sight; & as for determin"d visible inches, feet, &c., there can be no such thing obtain"d by the meer act of seeing-abstracted from experience, &c.
The greatness _per se_ perceivable by the sight is onely the proportion any visible appearance bears to the others seen at the same time; or (which is the same thing) the proportion of any particular part of the visual orb to the whole. But mark that we perceive not it is an orb, any more than a plain, but by reasoning.
This is all the greatness the pictures have _per se_.
Hereby meere seeing cannot at all judge of the extension of any object, it not availing to know the object makes such a part of a sphaerical surface except we also know the greatness of the sphaerical surface; for a point may subtend the same angle wth a mile, & so create as great an image in the retina, i.e. take up as much of the orb.
Men judge of magnitude by faintness and vigorousness, by distinctness and confusion, with some other circ.u.mstances, by great & little angles.
Hence "tis plain the ideas of sight which are now connected with greatness might have been connected wth smallness, and vice versa: there being no necessary reason why great angles, faintness, and distinctness without straining, should stand for great extension, any more than a great angle, vigorousness, and confusion(227).
My end is not to deliver metaphysiques altogether in a general scholastic way, but in some measure to accommodate them to the sciences, and shew how they may be useful in optiques, geometry, &c.(228)
Qu. Whether _per se_ proportion of visible magnitudes be perceivable by sight? This is put on account of distinctness and confusedness, the act of perception seeming to be as great in viewing any point of the visual orb distinctly, as in viewing the whole confusedly.
Mem. To correct my language & make it as philosophically nice as possible-to avoid giving handle.
If men could without straining alter the convexity of their crystallines, they might magnify or diminish the apparent diameters of objects, the same optic angle remaining.
The bigness in one sense of the pictures in the fund is not determin"d; for the nearer a man views them, the images of them (as well as other objects) will take up the greater room in the fund of his eye.
Mem. Introduction to contain the design of the whole, the nature and manner of demonstrating, &c.
Two sorts of bigness accurately to be distinguished, they being perfectly and _toto caelo_ different-the one the proportion that any one appearance has to the sum of appearances perceived at the same time wth it, wch is proportional to angles, or, if a surface, to segments of sphaerical surfaces;-the other is tangible bigness.
Qu. wt would happen if the sphaerae of the retina were enlarged or diminish"d?
We think by the meer act of vision we perceive distance from us, yet we do not; also that we perceive solids, yet we do not; also the inequality of things seen under the same angle, yet we do not.
Why may I not add, We think we see extension by meer vision? Yet we do not.
Extension seems to be perceived by the eye, as thought by the ear.
As long as the same angle determines the _minimum visibile_ to two persons, no different conformation of the eye can make a different appearance of magnitude in the same thing. But, it being possible to try the angle, we may certainly know whether the same thing appears differently big to two persons on account of their eyes.
If a man could see ... objects would appear larger to him than to another; hence there is another sort of purely visible magnitude beside the proportion any appearance bears to the visual sphere, viz. its proportion to the M. V.
Were there but one and the same language in the world, and did children speak it naturally as soon as born, and were it not in the power of men to conceal their thoughts or deceive others, but that there were an inseparable connexion between words & thoughts, so yt _posito uno, ponitur alterum_ by the laws of nature; Qu. would not men think they heard thoughts as much as that they see extension(229)?
All our ideas are adaequate: our knowledge of the laws of nature is not perfect & adaequate(230).
(M388) Men are in the right in judging their simple ideas to be in the things themselves. Certainly heat & colour is as much without the mind as figure, motion, time, &c.
We know many things wch we want words to express. Great things discoverable upon this principle. For want of considering wch divers men have run into sundry mistakes, endeavouring to set forth their knowledge by sounds; wch foundering them, they thought the defect was in their knowledge, while in truth it was in their language.
Qu. Whether the sensations of sight arising from a man"s head be liker the sensations of touch proceeding from thence or from his legs?
Or, Is it onely the constant & long a.s.sociation of ideas entirely different that makes me judge them the same?