Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . eare many modes of graduating speaking-rods so as to make the divisions legible at the greatestdistance at which the rod is such rods can be purchasedof instrument-makers, the easiestway to obtain them being for thelevelman to divide and paint themhimself. They consist usually ofwell-seasoned pine ^ to i inch inthickness and from 3 to 5 inchesin width. The figures are made aslarge as possible, so as to be legible,and various markings are introd
Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . eare many modes of graduating speaking-rods so as to make the divisions legible at the greatestdistance at which the rod is such rods can be purchasedof instrument-makers, the easiestway to obtain them being for thelevelman to divide and paint themhimself. They consist usually ofwell-seasoned pine ^ to i inch inthickness and from 3 to 5 inchesin width. The figures are made aslarge as possible, so as to be legible,and various markings are introducedbetween these or in the shapes ofthe figures themselves, so that theeye shall have a guide whereby todivide the spaces (Figs. 81 and 97).In order to get more accuratea work from a speaking-rod the level Fig. 97.—Speaking Level- should have tJiree horizontal cross- liairs m the diaphragm, and thelevelman should tell the rodman where to place his finger orpencil, and the latter should record this as an approximatecheck on the reading. The levelman should then read eachof the three cross-hairs and record its reading separately, so. TURNIiXG-POINTS. 15 that by taking a mean of these he has a greater check on thereading observed and gets a niore accurate determination ofthe height than by reading one cross-hair only. 134. Turning-points.—In rough leveling it is of littleconsequence what manner of turning-point be used. Theturning-point may be on a pebble or other hard object onthe ground, or on a short stake driven into the ground, or ahatchet laid on the ground. Where accurate work is attempteda better turning-point must be employed, as the top of a rail,the head of a hatchet the blade of which is driven firmly intothe ground, or a spike-shaped hammer, or a large stone whichis well embedded in the ground. For precise work, however, these forms of turning-pointare not sufificiently stable. Along railroads the best pos-sible turning-point is on top of the rail at a point clea
Size: 1162px × 2150px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., book, bookcentury1900, bookdecade1900, bookpublishernewyorkjwiley
