. 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 . bly be found to be a little too large,and the other a little too small. The average between the two isthe exact area of the figure, and is more to be depended on thanthe results of measurements made by scale and calculation in theusual way, A careful operator, in using the planimeter, willalways take the average of two tracings in this manner; but whenhe experiences the rapidity with which this may be done,
. 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 . bly be found to be a little too large,and the other a little too small. The average between the two isthe exact area of the figure, and is more to be depended on thanthe results of measurements made by scale and calculation in theusual way, A careful operator, in using the planimeter, willalways take the average of two tracings in this manner; but whenhe experiences the rapidity with which this may be done, he willfind the trouble as nothing in comparison with the harassing labourof calculating by scale and multiplication. Mr. Miller of Woolwich has devised a very useful modificationof the common jointed rule. This instrument is termed a radiator, and our engraving, fig. 36, represents a portion ofit in plan, whilst fig. 37 is an end elevation. The inner edges ofthe legs are used as rulers, and the joint has a transparent 2b 194 THE PRACTICAL DRAUGHTSMANS centre, A, which is placed directly over the point to be drawn graduated arc, e, is supplied, and the brass legs are furnished. < with sockets, which admit of any length of ruler being radiator is applicable to the following purposes :— For drawing lines in perspective, or geometrical drawing, to apoint or centre; for setting off angles as a protractor; for a right-angled triangle, or any other angles ; and for setting out po gonsof different numbers of sides. In using it, the centre of the glassis placed over the centre to be drawn to, and a line is drawn alongthe inner edge of the ruler from the point required. Whenmany lines are to be drawn to one centre, the hand must be placedupon one leg, to allow the other to be moved to the severalpoints. Two forms of protractors, or instruments for setting off ormeasuring angles have already been described; * a third, andmuch approved form, consists of a circular bar d
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Keywords: ., bookcentury1800, booksubjectdecorativearts, booksubjectdrawing
