. 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 . for the smaller and more delicate work which he is constantlycalled upon to execute- Fig. 17 is a front, and fig. 18 a sideelevation of a very neat form of jointed bow compasses witha pen. The main joint is embraced by two eye plates, towhich a small handle is attached. A portion of this handle ismilled, to give control over the instrument and facility in turningit. It will also be observed that the centre p
. 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 . for the smaller and more delicate work which he is constantlycalled upon to execute- Fig. 17 is a front, and fig. 18 a sideelevation of a very neat form of jointed bow compasses witha pen. The main joint is embraced by two eye plates, towhich a small handle is attached. A portion of this handle ismilled, to give control over the instrument and facility in turningit. It will also be observed that the centre point is a needle,held by a small screw, in a socket formed in the leg of theinstrument. This arrangement affords a means of adjustmentas to length, whilst the point can easily be replaced if acci-dentally broken. Compasses of the larger size are sometimesmade with similar needles, but this refinement is considered bymost draughtsmen as unnecessary in them, if the needle isnot indeed inferior to the ordinary point, which, from its greater Fig-. 13. Fig;. 15. Fig. size and strength, isless liable to legs of the bow-pen compasses arejointed. Fig. 19 is afront elevation of aninstrument preciselysimilar to the last, ex-cept that it has a pen-cil instead of a compasses re-quire to be adjusted to any desired radius by the direct action ofthe hand. In work where great accuracy and minuteness is calledfor, it will often be found a very tedious matter to obtain a trueadjustment in this manner, particularly if the joints of the instru-ment are not in perfect working condition. This difficulty is gotover in what are termed spring, or screw bow compasses:. BOOK OF INDUSTRIAL DESIGN. 189 Fig. 20 is a side, and fig. 21 a front view of a pair of pen com-passes of this class. The use of such instruments is confined to
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