Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . will be brieflycharacterized. The pantograpJi is a parallel linked-motion apparatus forenlargement or reduction of maps. It is of occasional assist-ance in the reduction or enlargement of compiled map material,and is constructed on the theory of parallelograms. (Fig. 149.)The pantograph is, however, a comparatively inaccurateinstrument because of the great play between the variousparts. If accuracy is attempted, none but the most expensiveand heavily const
Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . will be brieflycharacterized. The pantograpJi is a parallel linked-motion apparatus forenlargement or reduction of maps. It is of occasional assist-ance in the reduction or enlargement of compiled map material,and is constructed on the theory of parallelograms. (Fig. 149.)The pantograph is, however, a comparatively inaccurateinstrument because of the great play between the variousparts. If accuracy is attempted, none but the most expensiveand heavily constructed instruments should be used. Thereis an inconvenient variety of combinations in the adjustmentand use of this instrument. The essentials are that the fixed, 47^ TOPOGRAPHIC DKAVVIXG. the tracing, and the copying points shall lie in a straight lineon at least three sides of the jointed parallelograin. Two very useful instruments to the topographer areproportional dividers and three-legged dividers, the first ofwhich is very serviceable in the reduction or enlargement ofsmall portions of maps, and the second in transferring work. Fig. 149.—Pantograph. from one map to another. In this operation two of the legsare set on fixed points common to both maps, as the inter-sections of projection lines, and the third is used as a pointerto transfer the position desired. This instrument is especiallyuseful in the transferring and adjustment of lines from thetraverse sheets (Fig. 2) to the sketch sheets on which theyare to be adjusted to the triangulation positions (Fig. 3). For the construction of projections the topographer needsa first-class beam compass and an accurately graduated steelscale. The ordinary triangular boxwood scale is well gradu-ated and is useful in the projection of very small scale-maps;but for larger ones a long steel scale, preferably divided tothe scale of the map work, will give much more satisfactoryresults. The use of vernier protractors is fully describe
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