Chapter I: THE SIGHT-POINT.—Let ABCD, Fig. 1., be your sheet of paper, the

larger the better, though perhaps we may cut out of it at last only a small piece for our picture, such as the dotted circle _NOPQ_. This circle is not intended to limit either the size or shape of our picture: you may ultimately have it round or oval, horizontal or upright, small or large, as you choose. I only dot the line to give you an idea of whereabouts you will probably like to have it; and, as the operations of perspective are more conveniently performed upon paper underneath the picture than above it, I put this conjectural circle at the top of the paper, about the middle of it, leaving plenty of paper on both sides and at the bottom. Now, as an observer generally stands near the middle of a picture to look at it, we had better at first, and for simplicity’s sake, fix the point of observation opposite the middle of our conjectural picture. So take the point _S_, the center of the circle _NOPQ_;—or, which will be simpler for you in your own work, take the point _S_ at random near the top of your paper, and strike the circle _NOPQ_ round it, any size you like. Then the point _S_ is to represent the point _opposite_ which you wish the observer of your picture to place his eye, in looking at it. Call this point the “Sight-Point.”