as a medium between the large compasses and the spring-bow set.

The most important part of a pair of compasses is the head, which forms the hinged joint. There are two forms of joints: the tongue-joint, as shown in the left-hand view in Fig. 3, in which the head of one shank has a tongue, generally made of steel, which moves between two lugs on the other shank, and the pivot joint, as shown in the right-hand view in Fig. 3, in which each shank is reduced to half its thickness at the head. These shanks are

the fingers before and after describing a circle. The non-removable leg of the compass should carry a needle-point, that may be easily replaced if lost or damaged, and it should have a shoulder to prevent the point from sinking into the paper beyond a certain depth. The needle-point should also be capable of being adjusted in or out, and fastened securely at any desired point, thus mak

surrounded by a clamp or yoke, which carries two cone-pointed set-screws, one in each side, the points of these screws working in countersunks in the yoke. The yoke is provided with a milled or knurled handle to manipulate the compass. The head joint of the compass should move freely and evenly throughout its entire movement, and not stiff at one point and loose at another. It should also be tight enough in the joint to hold its adjustment when once set. Figure 4 shows the method of holding a compass, and the correct position of

Fig. 4 Correct Manner of Holding a Compass.

ing the leg of the compass a little longer or shorter as may be desired.

The socket for the lead in the pencil-point should hold the lead firmly without the necessity of wedging it in the socket by means of paper or small pieces of wood.

When first adjusting the compass for use, place the pen-point in the instrument and securely clamp it in place, firmly against the shoulder of

the socket, then adjust the needle-point so that its point is even with that of the pen. When once properly adjusted the needle-point should not be changed. The needle-point is usually made with a cone-point at one end and a fine shoulderedpoint at the other. The cone-point should never be used, as it makes too large a hole in the drawing paper.

Hair Spring Dividers. Dividers such as are shown in Fig. 5 are used for laying off equal distances and for transferring measurements from one part of a drawing to another, or from one drawing to another. They consist of steel points

the purpose of describing small circles and laying off distances of very small dimensions and are very convenient for these purposes. Any form of spring-bow instruments with interchangeable or removable legs will be found very unsatisfactory. The legs should be made of one piece of steel, to which the handle is attached. Any instrument in which the legs are separate pieces fastened to the

Fig. 5 Hair Spring Dividers.

set in German silver shanks which are hinged together. The joints of the dividers should work smoothly, the legs come close together, and the steel points should be sharp and of the same length. One of the legs of the dividers has a spring controlled by an adjustable thumb-nut. By means of this device, from which the instrument gets its name, the adjustable leg may be moved a trifle after the rough or approximate adjustment of the dividers has been made.

Spring-bow Instruments. The spring-bow dividers, pencil and pen, as shown in Fig. 6, are for

Fig. 6-Spring-bow Instruments.

shank are undesirable, because the parts are liable to become loose. The spring-bow dividers are used like the hair-spring dividers, for the spacing of distances, they have the advantage of being fixed in any position so that there is no liability of a change of measurement by the handling of the instrument. When spacing distances the divider