. The practical draughtsman's book of industrial design, and machinist's and engineer's drawing companion: forming a complete course of mechanical, engineering, and architectural drawing . ant on the piece, A. By this apparatusany angles may be measured and laid off by the quadrant, andtransferred to any point on the paper without the aid of anyadditional instrument, as the whole instrument may be moved toany desired point on the straight-edge, c, without any shift ofposition with reference to the meridian line or starting additional scales on the right angle straight-edges, j, thei
. The practical draughtsman's book of industrial design, and machinist's and engineer's drawing companion: forming a complete course of mechanical, engineering, and architectural drawing . ant on the piece, A. By this apparatusany angles may be measured and laid off by the quadrant, andtransferred to any point on the paper without the aid of anyadditional instrument, as the whole instrument may be moved toany desired point on the straight-edge, c, without any shift ofposition with reference to the meridian line or starting additional scales on the right angle straight-edges, j, theinstrument, may be employed, as an offset scale, for plotting sur-veys and laying down sections. One of the most economically useful instruments of thedraughtsman is the Pentagraph; but it is one which requiressuch extreme accuracy and truthfulness in its construction, thatits consequent cost puts it out of the reach ef the majority ofthose who need it. By means of it, drawings may be copied onan enlarged or a reduced scale, by the mere action of carryinga tracing point over the lines of the original drawing. Themotion of the tracing point is communicated to the delineating Fig. r>- ?, ?!*£? pencil by the angular movements of a series of levers oscillatingupon a fixed centre. If one arm of a lever is twice as long as theother, the arc described by its extremity will be twice as great,whatever be the extent of the movement. In this case, however,the radii of the arcs would be uniform, and an arrangement isrequired, providing for the increase or decrease in length of thetwo radii, but in such a manner that they shall continually BOOK OP INDUSTRIAL DESIGN. 195 be in the same proportion to each other. This is effected bymaking the main lever with joints midway between the extremi-ties and the centre of mo-tion. It is, necessary, how- Fis- , that the outer jointsof the lever should be main-tained constantly parallel
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Keywords: ., bookcentury1800, booksubjectdecorativearts, booksubjectdrawing
