If you want to represent a figure on a wall, the wall being foreshortened, while the figure is to appear in its proper form, and as standing free from the wall, you must proceed thus:  have a thin plate of iron and make a small hole in the centre; this hole must be round.  Set a light close to it in such a position as that it shines through the central hole, then place any object or figure you please so close to the wall that it touches it and draw the outline of the shadow on the wall; then fill in the shade and add the lights; place the person who is to see it so that he looks through that same hole where at first the light was; and you will never be able to persuade yourself that the image is not detached from the wall.

[Footnote:  uno piccolo spiracelo nel mezzo.  M. RAVAISSON, in his edition of MS. A (Paris), p. 52, reads nel muro—­evidently a mistake for nel mezzo which is quite plainly written; and he translates it "fait lui une petite ouverture dans le mur," adding in a note:  "les mots ‘dans le mur’ paraissent etre de trop.  Leonardo a du les ecrire par distraction" But ’nel mezzo’ is clearly legible even on the photograph facsimile given by Ravaisson himself, and the objection he raises disappears at once.  It is not always wise or safe to try to prove our author’s absence of mind or inadvertence by apparent difficulties in the sense or connection of the text.]

526.

TO DRAW A FIGURE ON A WALL 12 BRACCIA HIGH WHICH SHALL LOOK 24
BRACCIA HIGH.

If you wish to draw a figure or any other object to look 24 braccia high you must do it in this way.  First, on the surface m r draw half the man you wish to represent; then the other half; then put on the vault m n [the rest of] the figure spoken of above; first set out the vertical plane on the floor of a room of the same shape as the wall with the coved part on which you are to paint your figure.  Then, behind it, draw a figure set out in profile of whatever size you please, and draw lines from it to the point f and, as these lines cut m n on the vertical plane, so will the figure come on the wall, of which the vertical plane gives a likeness, and you will have all the [relative] heights and prominences of the figure.  And the breadth or thickness which are on the upright wall m n are to be drawn in their proper form, since, as the wall recedes the figure will be foreshortened by itself; but [that part of] the figure which goes into the cove you must foreshorten, as if it were standing upright; this diminution you must set out on a flat floor and there must stand the figure which is to be transferred from the vertical plane r n[Footnote 17:  che leverai dalla pariete r n.  The letters refer to the larger sketch, No. 3 on Pl.  XXXI.] in its real size and reduce it once more on a vertical plane; and this will be a good method [Footnote 18:  Leonardo here says nothing as to how the image foreshortened by perspective and thus produced on the vertical plane is to be transferred to the wall; but from what is said in Nos. 525 and 523 we may conclude that he was familiar with the process of casting the enlarged shadow of a squaring net on the surface of a wall to guide him in drawing the figure.