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P. 107 them, by the prejudgment of the mind from the
better authority of feeling, or some other persuasive motive. But surely this extraordinary perversion of the sight would not have been suffered, did it not tend to great and necessary purposes, in rectifying some deficiencies which it would otherwise be subject to (though we must own at the same time, that the mind itself may be so imposed upon as to make the eye see falsely as well as truly) for example, were it not for this controul over the sight, it is well known, that we should not only see things double, but upside down, as they are painted upon the retina, and as each eye has a distinct sight. And then as to distances; a fly upon a pane of glass is sometimes imagined a crow, or larger bird afar off, till some circumstance hath rectified the mistake, and convinced us of its real size and place.
Hence I would infer, that the eye generally gives its assent to such space and distances as have been first measured by the feeling, or otherwise calculated in the mind : which measurements and calculations are equally, if not more, in the power of a blind man, as was fully experienced by that incomparable mathematician and wonder of his age, the late professor Sanderson.
By pursuing this observation on the faculties of the mind, an idea may be formed of the means by which we attain to the perception or appearance of an immense space surrounding us; which cavity, being
subject to divisions and subdivisions in the mind, is P. 108 afterwards fashioned by the limited power of the eye,
first into a hemisphere, and then into the appearance
of different distances, which are pictured to it by means of such dispositions of light and shade as shall next be described. And these I now desire may be looked upon, but as so many marks or types set upon these distances, and which are remembered and learnt by degrees, and when learnt, are recurred to upon all occasions.
If permitted then to consider light and shades as types of distinction, they become, as it were, our materials, of which prime tints are the principal; by these, I mean the fixed and permanent colours of each object, as the green of trees, &c. which serve the purposes of separating and relieving the several objects by the different strengths or shades of them being opposed to each other *.
The other shades that have been before spoken of, serve and help to the like purposes when properly opposed; but as in nature they are continually fleeting and changing their appearances, either by our or their situations, they sometimes oppose and relieve, and sometimes not, as for instance; I once observed the tower-part of a steeple so exactly the colour of a light cloud behind it, that, at the distance I stood, there was not the least distinction to be made, so that the spire (of a lead colour) seemed suspended in the air; but had a cloud of the like tint with the steeple, supplied the place of the white one, the tower would then have been relieved and distinct, when the spire would P. 109 have been lost to the view.
* Fig. 86. T. p. 2.
Nor is it sufficient that objects are of different colours or shades, to shew their distances from the eye, if one does not in part hide or lay over the other, as in fig. 86.
For as fig. * the two equal balls, though one were black and the other white, placed on the separate walls, supposed distant from each other twenty or thirty feet, nevertheless, may seem both to rest upon one, if the tops of the walls are level with the eye; but when one ball hides part of the other, as in the same figure, we begin to apprehend they are upon different walls, which is determined by the perspective': hence you will see the reason, why the steeple of Bloomsburychurch, in coming from Hamstead, seems to stand upon Montague-house, though it is several hundred yards distant from it.
Since then the opposition of one prime tint or shade to another, hath so great a share in marking out the recessions, or distances in a prospect, by which the eye is led onward step by step, it becomes a principle of consequence enough to be further discussed, with regard to the management of it in compositions displaced by the alteration of light, for which reason, designs done in two prime tints only, will sufficiently represent all those recessions, and give a just keeping to the representation of a prospect, in a print; whereas, the oppositions in nature, depending, as has been before hinted, on accidental situations and uncertain incidents, do not always make such pleasing composition, and would therefore have been very often deficient, had nature worked in two colours only; for which reason she hath provided an infinite number of materials, not only by way of prevention, but to add lustre and beauty to her works.
of nature, as well as art. As to the management of P. 110 it, when seen only from one point, the artist hath the
advantage over nature, because, such fixed dispositions of shades as he hath artfully put together, cannot be
* Fig. 90. T. p. 2.
1 The knowledge of perspective is no small help to the seeing objects truly, for which purpose Dr. Brook Taylor's Linear Perspective made easy to those who are unacquainted with geometry, may be of inost service.
By an infinite number of materials, I mean colours and shades of all kinds and degrees; some notion of which variety may be formed by supposing a piece of white silk by several dippings gradually dyed to a black; and carrying it in like manner through the prime tints of yellow, red, and blue; and then again, by making the like progress through all the mixtures that are to be made of these three original colours. So that when we survey this infinite and immense variety, it is no wonder, that, let the light or objects be situated or changed how they will, oppositions seldom miss: nor that even every incident of shade should sometimes be so completely disposed as to admit of no further beauty, as to composition; and from P. 111 whence the artist hath by observation taken his principles of imitation, as in the following respect.
Those objects which are intended most to affect the eye, and come forwardest to the view,must have large, strong, and smart oppositions, like the fore-ground in
fig. *, and what are designed to be thrown further off, must be made still weaker and weaker, as expressed in figures 86, 92, and 93, which receding in order make a kind of gradation of oppositions; to which, and all the other circumstances already described, both for recession, and beauty, nature hath added what is known by the name of aerial perspective; being that interposition of air, which throws a general soft retiring tint over the whole prospect; to be seen in excess at the rising of a fog. All which again receives still more distinctness, as well as a greater degree of variety, when the sun shines bright, and casts broad shadows of one object upon another; which gives the skilful designer such hints for shewing broad and fine oppositions of shades, as give life and spirit to his performances.
BREADTH of shade is a principle that assists in making distinction more conspicuous; thus fig. †, is better distinguished by its breadth or quantity of shade, and viewed with more ease and pleasure at any distance, than fig. 1, which hath many, and these but narrow shades between the folds. And for one of the noblest instances of this, let Windsor-castle be
viewed at the rising or setting of the sun. P. 112' Let breadth be introduced how it will, it always
gives great repose to the eye; as on the contrary, when lights and shades in a composition are scattered about in little spots, the eye is constantly disturbed, and the mind is uneasy, especially if you are eager to