device, called a compensator (fig. 15-41), makes thispossible. The compensator is suspended on fine,nonmagnetic wires. The action of gravity on thecompensator causes the optical system to swing intothe position that defines a horizontal line of sight. Thishorizontal line of sight is maintained despite a slightout-of-level telescope or even a slight disturbanceoccurs on the instrument.TRIPODThe tripod (fig. 15-42) is the base or foundationthat supports the level instrument and keeps it stableduring observations. A tripod consists of a head towhich the instrument is attached, three wooden ormetal legs that are hinged at the head, and pointedmetal shoes on each leg to be pressed or anchored intothe ground to achieveIn setting up thestrap from around thea firm setup.tripod, loosen the restrainingthree legs. An effective way toset the tripod down is to grip it with two of the legsclose to your body while you stand over the pointwhere the setup is required. By using one hand, pushthe third leg out away from your body until it is about50 to 60 degrees with the horizontal. Lower the tripoduntil the third leg is on the ground. Place one hand oneach of the first two legs, and spread them while takinga short backward step, using the third leg as a pivotpoint. When the two legs look about as far away fromthe mark as the third one and all three are equallyspaced, lower the two legs and press them into theFigure 15-42.—Tripods.Figure 15-41.—Self-leveling level compensator.15-24
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