The operation of setting out lines upon walls or other surfaces is by no means easy. It involves care and judgment, a quick eye, and a very steady hand. It is the indispensable preliminary before ornamental work or illumination can be executed, as it can alone correctly give the forms of panels, borders, &c., for which cartoons may have to be prepared. Lines may be either drawn with pencil or prepared charcoal, or chalk, or else struck by means of a chalked string. For lines which are vertical, a weight called a plumb-bob must be attached to one end of the string. The best shape for this is that of half an egg, as the flat side will then lie close to the wall. Two persons are required in setting out these lines,--one working above and the other below. The one at the top marks the points at the distance each line is required to be from others. The string being chalked either black or white,--according as the line has to show upon a light or dark ground,--he holds it to one of the points, and lets fall the weighted end, which, when quite steady, the person who is below strains tight, and raising the string between his finger and thumb in the middle, lets it fall back sharply on the wall. The result, if carefully executed, is a perfectly straight and vertical line. The horizontal lines require to be drawn with a straight-edge or ruler, and may be either set out at a true right angle to the vertical lines geometrically by the intersection of arcs of circles, or by a large square, or may be defined, irrespectively of mathematical correctness, by measuring up or down from a ceiling or floor line. The distances apart are as before measured out, but in long lines must be marked as many times as the length of the straight-edge may require. This being set at each end to the points marked, the line is drawn along it. Circles and curved lines may be struck from their proper centres with large wooden compasses, one leg carrying a pencil. Drawing lines with the brush requires great practice. A straight-edge is placed upon the chalk lines, with the edge next the line slightly raised, and the brush, well filled with colour, drawn along it, just touching the wall, the pressure being never increased, and the brush refilled whenever it is near failing; but great care must be taken that it be not too full, as in that case it will be apt to blotch the line, or drop the colour upon the lower portions of the wall. Drawing lines in colour overhead upon a ceiling is even more difficult, and is beyond the capabilities of most amateurs.