Permit me, brother, to call your attention once more to the evident variations of the size of separate objects, according to their distances from the eye; which inclines me to think that a single figure would be affected by the rule you have given us, if one part of it were to be much nearer my eye that another, please to help me clearly through this idea.

Inconsiderate artists, before they have learned great importance and usefulness of perspective, fall into great errors for want of the thought you have given the subject, and this most frequently in portrait painting. Although many take a real measure of the face and features, which may answer a good purpose when a head only is to be painted yet in half lengths, or more where some variety of attitude should be an object of equal importance with the resemblance, the perspective or apparent size of each part, must supersede the absolute measurement. Attend to the position of the lady, (fig. 134), sitting opposite the eye which is represented as viewing her through the aperture of the frame FF, which is to contain the picture when finished. Suppose the surface to be glass instead of canvass, and that a real figure sat behind it as the drawing represents, the rays from the eye to her head must pass through the glass at a and s, which would give the prepare size the head should be drawn. The same rule will determine the size the hands should be in the picture.

But the right hand is so near the sectional plane or supposed glass, and the left at equal distance with the head, that there must be considerable difference in their size, when painted by the rule you have given.

And would not that make the right-hand look too large for the head and the left-hand?

This question passes as a reasonable one, with older artists than you, John. Perhaps you have not observed that the man on horseback, including both (fig. 115), are not higher than the elbow of the military figure in front; and in the chessboard (fig.101) the furthermost row of squares is not one-third the width of the front row. You must look back to our conversations on the subject of fore-shortening and proper point of distance, which with the other explanations I have given you, will make you the best answer possible: you should all observe, that one perfection in a picture demands the society of others. The truth of perspective alone would not establish the excellence of the picture- it is of so eminent a class, that all the perfections of art must unite therewith to evince its importance, and confirm their own. - What would a scientific general be without an intelligent as well as a brave staff? And what either, without as brave an army, all subordinate members of on body?

Then we are to consider PERSPECTIVE as the generalissimo of painting, I presume?

Whether our comparisons be strictly parallel or not, this I may repeat, THAT EVERY MOTION O F THE PENCH MUST BE LIABLE TO ERROR, unless directed by the eye; and the art of perspective is absolutely necessary to convey to a flat surface a true description of what is SEEN on the variegated surface of nature. Faulty perspective in pictures, bears, an exact comparison with faulty grammar in language; and a strict grammarian may prove the insufficiency of mere grammar, by writing grammatical nonsense, as a correct perspective may be found in a very nonsensical picture; but the fault would not be owing to the perspective truth; therefore, as the ingenious and learned Du Fresnoy, in his "Verse on Perspective", could never intend to excuse a painter for his ignorance of as absolute an essential throughout every part of a picture as correct grammar is throughout every part of language, I would seriously advise those who have advanced in the practice of painting under the flattering and deceiving impulse of "intuitive infallibility" to relinquish the delusion; and learn, from the knowledge of perspective, and her attendant elements, "HOW TO BEGIN, PROCEED, AND FINISH A PICTURE".

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Introduction.
On geometry and the use of the instruments.