Lay the 12-inch scale along the line so that the edge is parallel to it at a distance of 1 inch (or half the length of the small offset scale) from it. This should be carefully done, the beginning of the scale being exactly opposite the beginning of the line. Place a weight on each end of the scale so as to keep it steady. The offset scale may now be used to slide along the 12-inch scale, and the exact position of each point measured may be marked on the paper by means of a fine pencil. (See Fig. 59.) When these offset points are joined by

straight lines in pencil

they may be inked in, and the boundary is correctly delineated.

2 inches

3 inches

FIG. 58,

11⁄2 inches

B

All the survey lines and boundaries having first been drawn in in pencil they may be afterwards be inked in, in red for the survey or constructional lines, when these have to be shown, and in black for the boundaries.

Care should be taken to avoid drawing unnecessary lines so as to prevent erasure as much as possible; and when india-rubber is used it should only be rubbed one way and not backwards and forwards. All lines should be drawn from left to right, and it is necessary to avoid pressing the pen against the edge of the set square as it produces an uneven line, and a good line must always

be the same thickness throughout. For ordinary use an HH pencil is best. The degree of hardness is indicated by the number of H's and of softness by the number of B's. When an ordinary drawing is to be made it is sufficient to fasten the drawing paper to the board by means of pins only: but if an important drawing is to be made, it is necessary to glue the edges of the drawing paper to the board, having first damped the whole surface of the paper with a sponge. By this means the paper is

well strained.

When one arc of a circle has been described and it is required to determine a point in it by the intersection of another arc, it is only necessary to mark off the point of the latter without drawing the arc this saves drawing unnecessary lines.

Materials. Good materials should be used. For plans of importance use Whatman's best drawing paper.

The most used sizes are double elephant, demy, and imperial. For working drawings cartridge paper is good enough, but for finished drawings use Whatman's best, as they bear wetting and stretching without damaging, and take shading and colouring well.

Always draw on the right side of the paper, i.e. in the case of Whatman's, the side from which on holding a sheet to the light, the maker's name in watermark can be read; and in the case of cartridge paper, the smooth hard side.

Tracing Paper.-This is useful for making copies of plans for temporary use, but it tears easily.

Tracing cloth is much superior, but is rather expensive, the best costing about:

27" 30" 36" 40" 43"

54" wide.

Rolls of 22 yards

17/6 18/6 21/6 25/9 27/9 37/9 per roll.

A good cloth for general use, however, is supplied by Messrs. Thornton, Paragon Works, Manchester, as follows:

Rolls of 20 yards-width 30 inches, at 12s. 6d. ; width 40 inches, at 168. per roll.

Indian Ink should be used on tracing cloth as on all drawings. When colouring tracing cloth put the colour on the side opposite to that on which the ink lines are drawn. The colour will go on better when the tracing cloth has been either well rubbed with indiarubber or well dried by the fire.

Rubbing the surface over with french chalk will make the cloth take ink lines better or a little ox-gall may be put in the ink or colour, but this practice is not recommended.

Colours.-Plans of land are usually coloured all over, the character of each part being shown by some conventional sign. A good draughtsman needs few colours, and it should be remembered

that a surveyor's plan should never be coloured, but tinted. The following will be found to be quite sufficient : Crimson lake, prussian blue, burnt sienna, yellow ochre, Payne's gray, sap green, and light red.

In order to obtain an even surface on large areas it is best to damp the paper before applying the colour. Red sable brushes are better than camel's hair. For putting on washes on large surfaces a large brush is required and the colour must be prepared thin and of sufficient quantity to start with. Commence at the top part of the drawing and gradually spread it downwards as evenly as possible. If deep colour is required, put it on in layers, and not dark all at once. Do not go over the work with a second coat until the first is quite dry.

Drawing Compasses and Dividers (Fig. 60).-The best compasses have a sector joint instead of the long joint: this lessens the amount of friction and stiffness when the instrument is nearly closed, and

THORNTON

FIG. 60.

the compasses consequently move with equal pressure whether nearly closed or wide open.

Spring Bows.-These are required for describing small circles. Drawing Pen (Fig. 61).-The drawing pen consists of two blades of brass or electrum ending in steel nibs fixed to an ivory handle. In order to facilitate cleaning one blade is hinged to the other, so that it can be opened and cleaned. The ink should be inserted between the nibs with a piece of paper, and the pen held nearly vertical against the rule so that both nibs touch the paper.

T Squares (Fig. 62).—These should be an inch shorter than the length of the drawing-board on which they are to be used.

Set Squares.-These are best made of transparent material. They are of sizes from 4 inches to 16 inches, triangular in form with one angle a right angle, and the others 45° and 45°, 60° and 30°, or 67° and 221°.

Beam Compasses.-These are used for striking arcs of long radii. Very often when plotting large surveys at 1 chain and 2 chains to the inch, the lines are too long to admit of an ordinary pair of compasses being used to describe the arc. These compasses have a beam from 2 feet to 4 feet long. Two sockets are fitted to the beam, one is fixed and the other which carries a pencil point can be made to slide up and down and clamped to any length.

Proportional Compasses.-These are used for reducing or enlarging the area of a plan in a given proportion as explained later. They consist of two similar brass or electrum limbs, making a double pair of compasses with steel points A, B, C, D clamped by turning the milled-head screw. (See Fig. 63.)

When closed the limbs appear as one, and in this position the instrument is to be adjusted by moving the slide up or down the groove.

If the index line on the slide is set to the figure 2 on the righthand side and clamped by the screw E, then any distance marked off by A and B will be half the distance measured by C and D, and so on for the other figures.

The circumferences also of circles may be divided into any number of equal parts up to 20, in the same way.

On the other face of the compasses, divisions for plans and solids are marked.

For plans. If the index on the slide be set to 3, then the area of the square made by the longer points C and D will be three times the square made by the points A and B ; and so on for the other figures.

For solids.-Set the index on the slide to any number on the scale of solids; then the distance between the points C and D will give the side of a solid of so many times the content as the number indicates; and the distance between the points A and B will give the reduced side of the solid.