bubble remains centered in both positions. Now swing 90 and 

 simply bring the bubble to the center of its scale with the other set 

 of leveling screws. When using the 3-screw base, first swing 

 the striding level parallel to any two of the leveling screws, and in 

 the final step swing the longer axis of the vial over the third screw 

 and use that screyv alone for centering purposes. This process 

 adjusts the vertical axis to perfect verticality and at the same time 

 has made the telescope axis horizontal in all positions. 



Fig- 74 Showing: general equipment with Vertical Clamp, Telescope 



Bubble, Vertical Circle (open or closed guard as desired,) with 



one Double Vernier; covered under the No. 4SS 4/4-ln., 



the No. 505 s-in. and the No. 605 6-in. Theodolite. 



Note: For the method of closing this type of vertical circle against dust 

 or rain, see Fig. 71, p. 122. 



The striding level in such a case supercedes the transverse 

 plate bubble which may now be brought to the center of its scale 

 if it happens to be out of adjustment. In fact, if one had broken 

 both his plate bubbles, he might get along very nicely if he had 

 only a striding level and followed the above suggestions. Usually 



110 



