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trusted only, I suppose, on account of their disinterestedness.

I apprehend a good deal of this will look more like resentment, and a design to invalidate the objections of such as are not likely to set the faults of this work in the most favourable light; than merely for the encouragement, as was said above, of such of my readers, as are neither painters, nor connoisseurs ; and I will be ingenuous enough to confess something of this may be true; but, at the same time, I cannot allow that this alone would have been a sufficient motive to have made me risk giving offence to any; had not another consideration, besides that already alledged, of more consequence to the purpose in hand, made it necessary. I mean the setting forth, in the strongest colours, the surprising alterations objects seemingly undergo through the prepossessions and prejudices contracted by the mind.-Fallacies, strongly to be guarded against by such as would learn to see

objects truly! P. 6 Although the instances already given are

pretty flagrant, yet it is certainly true, (as a farther confirmation of this, and for the consolation of those, who may be a little piqued at what has been said) that painters of every condition are stronger instances of the almost unavoid

able power of prejudice, than any people whatever.

What are all the manners, as they are called, of even the greatest masters, which are known to differ so much from one another, and all of them from nature, but so many strong proofs of their inviolable attachmentto falsehood, converted into established truth in their own eyes, by self-opinion? Rubens would, in all probability, have been as much disgusted at the dry manner of Poussin, as Poussin was at the extravagant of Rubens. The prejudices of inferior proficients in favour of the imperfections of their own performances, is still more amazing. Their eyes are so quick in discerning the faults of others, at the same time they are so totally blind to their own! Indeed it would be well for us all, ifone of Gulliver's flappers could be placed at our elbows to remind us at every stroke how much prejudice and self-opinion perverts our sight.

From what has been said, I hope it appears that those, who have no bias of any kind, either from their own practice, or the lessons of others, are fittest to examine into the truth of the principles laid down in the following pages. But as every one may not have had an opportunity of being sufficiently acquainted with the instances, P., that have been given : I will offer one of a familiar kind, which may be a hint for their observ

ing a thousand more. How gradually does the eye grow reconciled even to a disagreeable dress, as it becomes more and more the fashion, and how soon return to its dislike of it, when it is left off, and a new one has taken possession of the mind ?-SO vague is taste, when it has no solid principles for its foundation!

Notwithstanding I have told you my design of considering minutely the variety of lines, which serve to raise the ideas of bodies in the mind, and which are undoubtedly to be considered as drawn on the surfaces only of solid or opake bodies: yet the endeavouring to conceive, as accurate an idea as is possible, of the inside of those surfaces, if I may be allowed the expression, will be a great assistance to us in the pursuance of our present enquiry.

In order to my being well understood, let every object under our consideration be imagined to have its inward contents scooped out so nicely, as to have nothing of it left but a thin shell, exactly corresponding both in its inner and outer surface, to the shape of the object itself: and let us likewise suppose this thin shell to be made up of very fine threads, closely connected together, and equally perceptible, whether the eye is supposed to observe them from without, or within; and we shall find the ideas of the two surfaces of this shell will naturally coincide.

The very word, shell, makes us seem to see both surfaces alike.

The use of this conceit, as it may be called P. 8 by some, will be seen to be very great, in the process of this work : and the oftener we think of objects in this shell-like manner, we shall facilitate and strengthen our conception of any particular part of the surface of an object we are viewing, by acquiring thereby a more perfect knowledge of the whole, to which it belongs: because the imagination will naturally enter into the vacant space within this shell, and there at once, as from a center, view the whole form within, and mark the opposite corresponding parts so strongly, as to retain the idea of the whole, and make us masters of the 'meaning of every view of the object, as we walk round it, and view it from without

Thus the most perfect idea we can possibly acquire of a sphere, is by conceiving an infinite number of straight rays of equal lengths, issuing from the center, as from the eye, spreading every way alike; and circumscribed or wound about at their other extremities with close connected circular threads, or lines, forming a true spherical shell.

But in the common way of taking the view of any opake object, that part of its surface, which fronts the eye, is apt to occupy the mind

alone, and the opposite, nay even every other part of it whatever, is left unthought of at that time: and the least motion we make to reconnoitre any other side of the object, confounds

our first idea, for want of the connexion of the · P.9 two ideas, which the complete knowledge of the

whole would naturally have given us, if we had considered it in the other way before.

Another advantage of considering objects thus merely as shells composed of lines, is, that by these means we obtain the true and full idea of what is called the outlines of a figure, which has been confined within too narrow limits, by taking it only from drawings on paper; for in the example of the sphere given above, every one of the imaginary circular threads has a right to be considered as an outline of the sphere, as well as those which divide the half, that is seen, from that which is not seen; and if the eye be supposed to move regularly round it, these threads will each of them as regularly succeed one another in the office of outlines, (in the narrow and limited sense of the word :) and the instant any one of these threads, during this motion of the eye, comes into sight on one side, its opposite thread is lost, and disappears on the other. He who will thus take the pains of acquiring perfect ideas of the distances, bearings, and oppositions of several material points and lines in

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