Adjustments of the Auxiliary Telescope 



Parallelism of the auxiliary sight line is to he secured when 

 attached to the top by firmly fastening the swivel hase to the "solar 

 table" so that no lost motion is apparent. Measure the distance 

 between the centers of the telescopes by taking a mean between the 

 inside and outside distances between the tubes. Mark off this 

 amount on a sheet of paper at, say, 100 ft. from the instrument, so 

 placed that the lower mark may be seen while the main telescope 

 is in a horizontal position. If the auxiliary does not cut the 

 upper mark, turn the worm in the hub, as shown in Figs. 106 and 

 107, until a coincidence is perfected. Turning the worm screw 

 tends to turn the telescope slightly in azimuth, hut this can be cor- 

 rected by the tangent screw just above. In our latest device for 

 securing parallelism, the worm thread and the steady pin mentioned 

 have been superseded by opposing capstan head screws in the 

 adjusting block just under, andintheline of, the auxiliary telescope. 

 These screws simply icgulate the position of the encasement which 

 contains the axis of the auxiliary. One is marked with an X. If 

 this is always set toward the ocular a uniformity of seating will 

 be guaranteed. To adjust the auxiliary then against the test mark, 

 simply turn the capstan studs in opposite directions and be certain to 

 take up all lost motion. 



When the auxiliary leaves our works, the cross wires are care- 

 fully collimated to the optical axis and should never thereafter be 

 molested, because the expedient of moving the cross w ires in the 

 test for parallelism is both theoretically and practically incorrect. 

 The analogy between this argument and that on the adjustment of 

 the dumpy level is marked. If one wishes to verify the collimation 

 adjustment, he may do so by revolving the auxiliary longitudinally 

 in a set of improvised wyes. The outside of the tube is not neces- 

 sarily concentric with the axis of the objective to the utmost degree 

 of precision, but the method is superior to any yet devised. 



The test for parallelism is in reality desirable only for slope 

 stake setting and unless the surveyor insists on reading vertical 

 angles with the auxiliary at the top, the adjustment is not indis- 

 pensable for mining work. If it is thought desirable for any reason 

 to secure parallelism when the auxiliary is applied to the side, it 

 may be accomplished by similar means. 



Unless the surveyor wilfully disregards the purpose of the prin- 

 ciple of interchangeability as laid down on pp. 1734, there is no 

 occasion for deep concern about any adjustments in the auxiliary 

 telescope for mining work except those of alignment, centering and 

 verticaiity of the vertical wire. 



The Alignment Adjustment is one which requires only a 

 simple mechanical manipulation just before each set of observations. 

 The adjustment is not a permanent one. If the auxiliary is at the 





