The Height Adjustment for the \\ yes, as well as slight 

 errors in the vertically of the spindle, are automatically compensated 

 at the moment of observation by the "Vertical Control". 



The normal position of the vertical adjustment may be secured 

 by centering the bubble over either set of leveling screws; revolve 

 180 on the vertical axis, correct half the bubble displacement with 

 the leveling screws and the other half with the vertical control. Re- 

 peat this test over both sets of leveling screws and secure in this 

 way a vertically in the vertical axis as well as a relationship between 

 the elements of the base bars that will keep the bubble centered 

 during an entire revolution. 



If the zero of the graduated 

 drum does not coincide with the 

 index line above, hold the knurled head 

 tightly with one hand and turn the grad- 

 uated drum against a concealed inner 

 spring with the other, until a coincidence 

 is perfected. The indices of the scale 

 above should now also coincide, as shown 

 in Fig. 7. If not, loosen the two small set 

 screws, which secure the scale plate, and 

 tap the same gently in the desired 

 direction. 



The scale above the drum is intended 

 only for a counter to record the number 

 of full revolutions, and to bring the base 

 bars back to normal position before set- 

 ting up at any succeeding station. Each 

 division on the drum represents 1/100$ ; 

 one complete revolution of the drum in 

 dines the telescope % % and two revolu- 

 tions \%, etc. The use of stadia wires 

 with any leveling instrument is always 

 attended with some risk of using the 

 wrong horizontal wire for leveling pur- 

 poses. With this instrument distances 

 may be determined with the gradienter, 

 as explained at page 28. 



The word "precise" in connection 

 with any instrument tends to convey the 

 impression of time wasted in locating in- 

 Consequential errors, but in this case the 

 word is justified in the mechanical means 

 . 7 provided to center the bubble accurately 



at the instant of observtion, irrespective of maladjustments in the 

 vertical axis. This is a highly desirable requirement under the 

 most ordinary circumstances. The use of this instrument in the 

 field is not attended with tedium or complication, and its substantial 

 construction as well as its reasonable price justify its adoption 

 where difficulties with the ordinal v \\ ye lu\el have been obseived. 



16 



