into a truly horizontal position without reference to the leveling 

 base. Taking into account the desired accuracy in the work, some 

 discretion should be exercised and some limit should be set as to 

 the amount of bubble error which may be rectified by this means 

 without a readjustment of the leveling base. 



A Bulls-Eye Level is placed on the base bar, CD, at the poin t 

 V. This is to be used only for the rough preliminary setting of the 

 vertical axis before the final precautions are taken in setting up the 

 instrument for work. It is assumed that if the vertical axis is 

 adjusted with the bulls-eye level, it will be set with sufficient 

 accuracy so that observations can be taken immediately by use of 

 the vertical control 



This instrument can be set up and operated without the 

 necessity of the operator changing his position. This is a very 

 great convenience for work in ; wamp lands, or under other unstable 

 conditions, and the telescope is short enough to give the operator a 

 wide sweep of field without shifting his weight. 



To use this instrument as an ordinary dumpy level, 

 very carefully secure a normal position for the vertical control, as 

 previously directed, then clamp the thumb screw shown in 

 Fig. 13 just at the right and just above the graduated drum. This 

 will keep the bubble axis and the sight-line permanently normal to 

 the vertical axis. 



In this case, as recommended for the dumpy level, more rapid 

 and satisfactory results may be obtained by use of the three-screw 

 base, as suggested in the illustration. 



PKRCKNTAr.K (,K. \DIK\TS 



The graduated drum may also be used for the observation or 

 establishment of percentage grades in railway or highway work, or 

 for the determination of distances by the gradienter method. 

 Example 



T<> establish a 1.65$ grade, for instance, secure n normal 

 position for the V. C., as directed above, and get the H.I. with 

 respect to the starting point by any convenient means. Each 

 division on the drum represents 1/100 / ; a single revolution, or 50 

 divisions, YI% and two revolutions, 1 %, etc. To lay off 1.65$, 

 therefore, turn the drum in elevation or depression as desired, three 

 involutions plus 15 extra divisions. 



24 



