The line xx gives the termination of the inside of the teeth, df that of the outside; the go, gf are projected towards points on the line aft, cor

responding to ab in fig. 36. The distances between the teeth are set off on the line eh to m, h} p, ¿, t, &c.; lines are drawn from these to the« point on the line aft, to which og converges; these lines are produced to meet the line eg in the points 1, 2, 3, 4, 5, &c. From these points, lines as 1, 6, 3, 7, 5, 9 are drawn to the point on the line aft, to which gf converges; these lines are terminated by the line df. From the points A, 8, v, &c., lines are drawn to the same point on aft, as 5, 9, &c., these being terminated by the line xx ; the points 6, 7, 9, &c., are then joined to these, as 2, &c. The pupil should put in the whole of the wheel as here given.

Mechanical drawings are reduced or enlarged quickest by means of what are termed 'proportional compasses/ If these are not available, 4 scales' should be drawn from the different figures. Thus, to reduce the drawing in

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