wheels, give them an exactly simultaneous motion, and these bands have a screw adjustment, K, by means of which they may be tightened.

The arms A and B are made to slide through boxes under the pulley wheels, and may be clamped at any proportion of their lengths in the same manner as the central beam, c, may be made to slide and clamp to the box K.

The arm B carries a tracing point, G, and the arm a carries a pencil point, D. The pencil-holder may be raised by means of a cranked lever, F, attached to a cord, E, which passes over the centre beam, and thence to the tracing point, G.

The two arms and the beam are divided into 200 equal parts, which are figured 100 each way from the centre, and may be read to 1000th by means of the verniers on the sliding-boxes.

There is a loose weight which may be attached when the instrument has been set, and the object of which is to steady it when there is a great difference in the proportions to which the instrument is being worked.

It will be observed that the pulley wheels give the easiest possible motion; these wheels should be of exactly equal diameter, and as they are turned in a lathe, this equality may be obtained to the greatest perfection.

To bring the instrument into adjustment, let the verniers be set to zero, which will bring them to the centres of the arms and of the central beam; place the arms at right angles to the beam, as near as you may guess, and make a mark with the tracer and pencil point, and turn the instrument round so as to bring the pencil point into the mark made by the tracer; by doing this you will make the tracer move to the mark previously made by the pencil, exactly if the instrument is in adjustment; if otherwise, the error in difference should be bisected, and the adjusting screws on the band should be moved until the tracing point comes exactly into the bisection.

CHAPTER XIII.

ELEMENTARY PLAN DRAWING.

MANAGEMENT OF DRAWING PAPER; MOUNTED PAPER-STRAINING DRAWING PAPER-STRAIGHT-EDGES-SCALES-DRAWING PENS AND INK

COLOURING PLANS.

THERE are two kinds of drawing paper used in the preparation of plans-mounted and unmounted; the mounted paper may be purchased of almost any length, sheet after sheet of various widths being pasted on linen, or on what is called 'union cloth;' and it is generally on this paper that railway plans are prepared. The paper, however, is generally of an inferior quality, and rather thin; for plans of a superior quality, where there is much drawing or colouring, it is better to order a few sheets of the best drawing paper to be mounted at some of the large stationery establishments, such as Spottiswoode's, Waterlow's, Vacher's, or Metchim's, all in Parliament Street; we mention these, because they have great facilities for executing an order at once; the dimensions of the paper used for this purpose are generally imperial, 30′′ × 22′′; atlas, 34" x 26"; double elephant, 40′′ × 27′′; antiquarian, 53" x 31".

Sometimes, however, we are placed in situations where we are obliged to mount our paper ourselves; this often occurs abroad. To mount paper on linen or calico, the cloth should be laid upon a large smooth board of sufficient width and length: the cloth should be damped, and the edges should be tacked down to the board, the tacks being pretty close together, and care should be taken not to pull upon the edges of the cloth; it should lay on the board just flat and smooth. Or we may lay a long flat rule about half an inch from the edges of the cloth, and glue

them down to the board, laying on the glue hot and rather thick, with a flat brush about a quarter of an inch wide; it is not difficult to do, but requires a little care not to strain the cloth; if it has been damped and laid flat, it will lay smoothly on the board.

Having laid down the cloth, the next operation is to lay on strong paste, with a large soft brush; in doing this, do not pull at the cloth with the brush, but work the paste well in; this will not only ensure a better contact with the paper, but will also prevent the cloth from shrinking.

The edges of the sheet of paper should be cut very straight, and if the paper is thick, the edge of the paper at the back may be thinned down with glass paper. The sheets of paper may now be laid down on the cloth, the sheets overlapping each other by about one-third of an inch; if the paper is large, it will take two persons to lay each sheet, and they must take care to lay the paper flat without pulling at the sheets. If the paper is thick, it is well to let it lay a few minutes after the paste is laid on, the sheet will then expand and will dry much smoother on the cloth; if the paper has not been well wetted, it will be apt to rise in bladders here and there over the cloth.

This done, the mounted paper should not be interfered with for a day at least, even in a warm climate; when dry, it should be cut off the board, but before it is used, it should if possible have a good ventilating, and be exposed to the sun, first on one side and then on the other. Fresh mounted paper is apt to contract very much. The cloth should be at least a couple of inches wider than the paper.

STRAINING DRAWING PAPER.

Straining a sheet of drawing paper on a drawing board appears one of the most simple things imaginable: but a little experience shows that it is not quite so easy as first thought. The drawing board should be clean and perfectly smooth, and when we have to produce a plan with more care than usual, it is well to examine the sheet held up to the light in order to see that it has no flaws. It is well to cut the edges of the paper straight and smooth,

STRAINING DRAWING PAPER.

219

with the help of a steel straight-edge, and pretty square. The best side of the paper is generally that on which we can read the water-mark in the corner, and this side should be kept for drawing on; the other side should be wetted with a sponge and clean water. We always begin wetting the sheet well at the centre at first, and gradually damping towards the edges, but we always leave about an inch at each edge untouched. When sufficiently damped, the paper will begin to bag, and this should be pretty equally all over the sheet, but perhaps a little more in the centre. As soon as the gloss arising from the damping with the sponge has passed off, the paper is ready to be strained.

We now require a long flat wooden ruler, a stout piece of glue, flat and straight, and a little boiling water.

We may now turn the paper over on the drawing-board, that is, with the wetted side downwards; do this quietly, without straining the paper, which on being turned over should be laid with its edges parallel to those of the drawing-board; if they do not come so at first, the paper should be quietly lifted bodily off, and then laid down so that the paper shall lay parallel with the board.

The flat ruler should now be laid on the paper at about half an inch from either of the longest sides, and be gently pressed down thereon, so as to hold it firm, but not so as though you wanted to press the wood into the paper; you may now dip one end of the glue into the boiling water, half an inch deep or so, so that it may be partly dissolved.

Beginning at the middle of the edge of the paper, pass the moistened glue once or twice along the turned-up edge of paper towards one of the ends, the ruler being of course held steady; then pass the glue again moistened from the middle of the edge towards the other end.

You may now put down the glue and take up an ivoryhandled knife, or the handle of a stiff paper-knife, or something of the kind, and pass it firmly along the glued border laid flat to the board, and still working from the centre towards either end; the rule should not be moved until this is done. If sufficient glue has been applied to

the paper, not too wet and not too thickly, the edge of the paper will now adhere flat to the board.

We may now move the ruler to the opposite longer, but not adjacent side, and serve it in the same manner; working from the opposite sides makes the pull on the paper when drying square with it; it would otherwise be oblique or askew. Having thus laid down the longer opposite sides we take to the shorter ones.

We have given the above simple instructions as for the large-sized paper, double elephant or antiquarian, for instance; and having laid down some hundreds of sheets, we know the suggestions are safe, and that by these means a large-sized sheet of paper may be laid down in a few minutes, to lay as tight as a drum and as smooth as

water.

STRAIGHT-EDGES.

Unless we use the T-square, probably a straight-edge is the first instrument we use on sheets of paper, to draw long straight lines. Straight-edges are generally made of steel, and are generally now what they are professedly sold for, that is, straight. When there is any doubt about it, one way to test is to lay it on a flat sheet of paper, and to draw a long straight line along one edge; then turn it end for end, and lay it on the line, and see if it coincides; then turn over the other side, and try it that way on the same line, and again end for end. Repeat the same operations by sliding it along the line, three-quarters and half-ways. If the line and the edge coincide throughout these trials, there is not much to fear. It is just possible, however, that the straight-edge may bulge inwardly or outwardly, on both sides and equally from the centre; to test this, we may draw the straight-edge about half an inch from the line and load it; we may then stretch a fine black silk thread as tightly as it will bear, from one end to the other of the line we have drawn, and if the two coincide, it will be another favourable test.

Another way to try them is to take two straight-edges, and rest them endways on a table, and bring two edges