Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . ther. A declinatoire accompanies the alidadeand is carried in a separate box or is sometimes attached as apart of the striding-level. The declinatoire box is oblong,with the sides parallel to the north and south lines and grad-uated to about 5 minutes on either side of the zero. The chief difference between this alidade and the oneused by the United States Geological Survey (Fig. 49) is thatthe straight-edge of the latter is 18 or 24 inches in length,with
Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . ther. A declinatoire accompanies the alidadeand is carried in a separate box or is sometimes attached as apart of the striding-level. The declinatoire box is oblong,with the sides parallel to the north and south lines and grad-uated to about 5 minutes on either side of the zero. The chief difference between this alidade and the oneused by the United States Geological Survey (Fig. 49) is thatthe straight-edge of the latter is 18 or 24 inches in length,with one edge beveled and graduated to the scale of map-work. The telescope is on a standard 4 inches high, has afocal distance of 15 inches and a power of 20 diameters, withan objective of if inches diameter. The telescope revolveshorizontally in a sleeve, with a stop for adjustment of verticalcollimation. Instead of two small levels attached to thestraight-edge, a single detached circular level is carried bythe topographer. The smaller telescopic alidade used by the United StatesGeological Survey (Fig. 51) on traverse and stadia work is. Fig. 51.—Telescopic Alidade. more like the Coast Survey alidade in having a shorter tele-scope and focal distance and a shorter straight-edge. Thevertical arc, instead of being graduated on the side and read-ing against a vernier as is customary with other surveying in- ADJUSTMENTS OF TELESCOPIC ALIDADE. I 59 struments, is a sector, which, instead of pointing downwards,points towards the rear or eyepiece of the telescope and isgraduated on its outer surface. This is read against a vernierfixed in such position that the reading may be made from oneposition of the observer at the eyepiece without his movingto the side of the plane-table as in ordinary instruments. 60. Adjustments of Telescopic Alidade.—There arepractically no adjustments to the plane-table and alidadeexcepting the adjustments of the latter for striding-level andcollimation. Adju
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