An excerpt from the beginning of the PREFACE: TO pore over all these matters Paolo would remain alone, seeing scarcely any one, and remaining almost like a hermit for weeks and months in his house with- out suffering himself to be approached. So wrote Vasari of Paolo Uccello. To many since Uccello's time this most elegant and agreeable art, as the author of the Jesuit's Perspective regarded it, has had fascinations, and much midnight oil has been burned by its votaries. The Jesuit's Perspective, a seventeenth-century work, was reprinted for the seventh time late in the eighteenth century, and its errors and shortcomings seem to have stimulated the sounder mathematicians of the time to literary activity. These writers carried the art to its perfection, so far as theory was concerned. They found vanishing-points for lines in all possible positions, matter how curiously inclined to the picture. To the author of the Jesuit this advanced part of the subject never once occurred; he even marks as accidental, vanishing-points on the horizon other than the point of sight. With only parallel perspective, it is small wonder that so tireless an author should seek to increase the usefulness of his science by facilitating, its manipulation, since he could t extend its bounds. Perhaps the most remarkable instance is that which he borrows from the sieur Gr. D. L. His object is always to get the result quickly, without confusion, without long working lines, and with as few of them as possible. Hence, in this case, he avoids the use of a line elevation for his heights, and avoids also coming continually down to his ground-line for his dimensions He marks six feet on his ground line as a scale, and divides the first into inches. This scale he runs back to the point of sight. Provided thus with a regularly diminishing scale, if at any point on the ground he wishes to take or raise a measurement, he has his scale diminished to its due extent at the very point. He merely draws a level line at the point, and this, as it crosses the scale, indicates where he has to set his dividers. Then, to avoid having a distance-point off his paper, or at least a great way off, he measures his distances within by a scale only one-fourth of the scale for the widths and heights of which we have just been speaking. His distance-point is quite near. It is, in fact, a fractional distance-point measuring fourfold; and how accessible it is the student will very soon find.