My dear brother, when will you begin to teach us perspective? You know I do not love a state of darkness; and you have told me that a painter might as well be blind, as ignorant of this most important branch of his art.

Indeed, my dear Eliza, it is of the very first importance, and is rather the main root, or foundation of truth, in a picture, than a branch. I am very happy to find you so earnestly disposed to study it; and if sister Ann is at leisure, and John will be attentive, I will now endeavour to make you acquainted with all the necessary rules and principles. I trust you will not allow doubts, or critical objections, to interrupt the information I shall offer you.

Why brother, you know I can draw and yet I do not understand perspective. What is it? Shall I be able to draw better when I have learned it?

You know, my dear boy, you have always something to copy form: which, it is granted, you imitate prettily; but what would you do without a drawing ready designed to your hand? The "attention" which George has recommended, will be the best means of obtaining an answer to your question.

That is well observed: and I shall proceed - First, to point out to you the general and distinguishing character of PERSPECTIVE; which is, THE REPRESENTATION OF OBJECTS AS THEY APPEAR, AGREEABLY TO THEIR REAL FORMS, DIMENSIONS, AND VARIOUS DISTANCES; BY DRAWING OR PAINTING ON A FLAT SURFACE: for you know that paintings, drawings, and prints, are all produced on flat surfaces, and yet on such flat surfaces, distance, height, width, depth, and the various appearances of all sorts of substances, "even the thin air", is perceived to bear so nearly the effect of reality, as oftentimes to deceive the imagination: and to produce this effect, successfully, A THOROUGH KNOWLEDGE of Perspective, and a very ingenious and judicious use of such knowledge is absolutely necessary. The EYE (the particulars of the construction of which you will learn when you study optics) is so wonderfully contrived, as to receive, at one view or action of sight, and comprehend, all the visible matter which may appear within a certain space (or under a certain angle, according to the technical term to be hereafter explained.): producing a perfect idea of the real forms seen, by an association of lines and angles totally different from their absolute or geometrical measurements. Yet the form of a true and judicious perspective representation will so perfectly agree with the knowledge conveyed by the absolute or geometric form, that the one will stand as an evidence or test of the truth of the other. Thus: In viewing a long walk, or a street (which we will suppose to be level, straight, parallel, and uniform in the buildings) it will appear to diminish according to the distance, converging towards a point at the furthest end-thus, therefore, a PERSPECTIVE REPRESENTATION WOULD DESCRIBE IT - yet would the drawing preserve and convey to the mind a perfect idea of the geometric and real forms presented to the view: this however, so very differently from the objects themselves, that there might be but one retiring or converging level line, that of the horizon, in the whole drawing, - and no two retiring parallel lines, except such as were really not so in the objects of view, but actually diverging from the sight in the same degree as real parallels appear to converge to it:-for, all other line that are seen parallel must be perpendicular lines, and parallel with the surface of the picture; all lines also that are parallel with the horizon must be drawn as seen.  
Now for an experimental proof.- Go to the window, and look stedfastly through the square of glass which is directly opposite to your face (you know the glass is a flat surface, and must be understood to constitute what is called the transparent plane in perspective); now, if you can keep yourself stationary, within reach of the glass, you may trace, with a pen, a proper perspective outline of the scene or objects in view: and by first laying a thin wash of gum water, or isinglass, on the pane, you may trace the scene with a black, or rather red chalk pencil; and then placing a piece of paper over it, you may trace it off as an outline to make a finished drawing from.

But, brother, you must tell us how to keep the eye in one position, as I perceive at once the success of the operation depends on that.

O sister, that may be contrived many ways! - I long to try to take a view by this method. I wonder painters do not use it: I really feel as if I wanted no further information on the subject..

This could not fail of truth for the outline of all stationary objects - but the sun shadows are continually changing as the day advances, while a true picture requires that every thing should be represented as seen at once, as when you look at a picture, which could not accomplish without receiving instruction, which will follow in its proper place.- A very complete apparatus has been made, by which to take views in outline corresponding with this method: and it is used where expedition, or a want of knowledge of art, makes is necessary: it may be called a "Master key" to perspective, and is named, "HAYTER'S PORTABLE PERSPECTIVE TRIPOD", which I have simplified and rendered very portable. But I directed you the tracing on the window, only to confirm your ideas on this leading first principle, that in every thing your draw, you are to conceive you are drawing, on a glass or transparent plane, objects which are supposed to be on other side. But you are not to sit down with these contrivances, if you intend to become acquainted with the art of painting, as it will be absolutely requisite for you to learn all the elements, beginning with a practical geometry (sufficient knowledge of which I shall refer you to in due order), and leave all the secondary means of picture-making to those who will not acquire the art of doing without them.

What is meant by " secondary means "?

ALL COPYING, whether by measuring, tracing, squaring, or pouncing: and all mechanical aids in making copies of pictures, because an original is previously provided, so that all the study, knowledge, and labour which is required to produce an original picture, is already prepared to the eye and hand of the copyist.

I believe, sister this is too hasty a conclusion, for by what I have somewhere read on the subject, engraving (although dependent on some mechanical means to obtain certain and correct outline of the subject of imitation) is one of the great departments of art, and may be as excellent, in its way as painting itself, and such good engravings as are done from pictures which are less correct in colouring than in light and shade, may be so far improvements on the originals. Engravers consider themselves as "translators of pictures into another language", and claim the merit of improving on many originals, with advantage to the subject.

Now, to convince you of the great advantage of a regular acquaintance with the Art of perspective, please to observe, that architects, after they have drawn the geometrical plans and elevations of a building, can (by due knowledge of this art, united with a tolerably good taste for landscape drawing) give very true pictures of intended buildings or improvements before they are begun, making due allowance for the effects of what is called Landscape-gardening, and they often convey good hints for that.

Yes, as perfectly as you could trace them on a transparent plane, after the whole is completely built and planted: and those architects who thoroughly understand perspective can make out geometrical plans and elevations from correct perspective pictures of buildings so truly as to enable them to erect exact copies of as much of the real edifice as is represented in the picture, for this plain and evident reason, - If a geometrical object present the means of making a true perspective picture of it such picture must contain the material evidences of the original geometrical elevation.

How delightful ! What an art it must be! - but I can't help thinking it very difficult.

Why, there seems to be a kind of prophetic power in perspective, if one is enabled to show the true picture of a place before it is built. I also have some serious apprehensions of the difficulty.

Never fear sisters. Attention and perseverance will surmount great difficulties; and perspective being attainable by rules, must not be classed among the greatest. I will do all in my power to make the whole as easy and pleasant as possible.

Then you know, Eliza, we shall be able to prophesy pictures without tracing.

And yet, for my part, I have conceived a great partiality to this drawing on a glass, for while at the window I could imagine the window frame to be a picture frame, and all I saw beyond appeared to be a PERFECT PICTURE. Do come again and look, Ann, and if you take my idea, you will be delighted: for though the scene is not composed of the most picturesque objects, yet only consider it, as I do a painting and tell me if ever you saw a better.

Oh Eliza, I almost envy you this step! It has now taken my imagination rightly. You may well call it a perfect painting, although the scene makes it a poor picture. Well, who could have thought we should ever feel so much pleasure in looking towards that dull street!

Now, sisters, if only a right idea of perspective has given you so much pleasure, you may fairly conclude that that a right knowledge of it is worth the study, for to study we must proceed: and I hope you will never quit any subject or suffer me, till you clearly understand me. And let me entreat you to follow my explanations attentively, inquiring freely about what is passing, but do not on too fast by looking forward, as that may tend to the sort of dispatch which must be considered more a desire to get rid of a lesson, than to become acquainted with it.

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On geometry and the use of the instruments.  
Concluding dialogue.