CA, enclosing a square inch. Divide each of these lines. into ten equal divisions, and number and letter them as shown. Draw also the diagonal lines A 1, a 2, B 3, and so on; then the distances from the line A C to the points of intersection of the diagonals with the horizontal lines represent hundredths of an inch. 100 100 100 Suppose, for example, we trace one diagonal line in its path across the figure, taking that which starts from A and ends at 1 on the top horizontal line; then where the diagonal intersects horizontal line 1, is from the line B D, and, from the line A C, while where it intersects horizontal line 2, is 98 from line B D, and 2 from line A C, and so on. If we require to set the compasses to inch, we set them to the radius of n, and the figure 3 on line B D, because from that 3 to the vertical line d 4 is or inch, and from that vertical line to the diagonal at n is seven divisions from the line CD of the figure. 67 100 6 100 In making a drawing to scale, however, it is an excellent plan to draw a line and divide it off to suit the required scale. Suppose, for example, that the given scale is one-quarter size, or three inches per foot; then a line three inches long may be divided into twelve equal divisions, representing twelve inches, and these may be subdivided into half or quarter inches and so on. It is recommended to the beginner, however, to spend all his time making simple drawings, without making them to scale, in order to become so familiar. with the use of the instruments as to feel at home with them, avoiding the complication of early studies that would accompany drawing to scale. dimension, such fraction not being marked on the lineal measuring rules at hand. Figure 224 represents a scale for finding minute fractions. Draw seven lines parallel to each other, and equidistanţ draw vertical lines dividing the scale into half-inches, as at a, b, c, etc. -8 equal halves, draw .9. 10 11 12 Fig. 224. Divide the first space e d int diagonal lines, and number the as in the figure. The distance of point 1, which is the intersection of diagonal with the second horizon: Point line, will be inch from vertical line e. CHAPTER X. PROJECTIONS. IN projecting, the lines in one view are used to mark those in other views, and to find their shapes or curvature as they will appear in other views. Thus, in Figure 225a we have a spiral, wound around a cylinder whose end is cut off at an angle. The pitch of the spiral is the distance A B, and we may delineate the curve of the spiral looking at the cylinder from two positions (one at a right-angle to the other, as is shown in the figure), by means of a circle having a circumference equal to that of the cylinder. The circumference of this circle we divide into any number of equidistant divisions, as from 1 to 24. The pitch A B of the spiral or thread is then divided off also into 24 equidistant divisions, as marked on the left hand of the figure; vertical lines are then drawn from the points of division on the circle to the points correspondingly numbered on the lines dividing the pitch; and where line 1 on the circle intersects line on the pitch is one point in the curve. Similarly, where point 2 on the circle intersects line 2 on the pitch is another point in the curve, and so on for the whole 24 divisions on the circle and on the pitch. In this view, however, the path of the spiral from line 7 to line 19 lies on the other side of the cylinder, and is marked in dotted lines, because it is hidden by the |