104 



The Adjustments of the Auxiliary Telescopes of 31 in ing 



Transits. 



The Detachable Side-Telescope. 



This telescope, illustrated on page 164, as ordinarily made, is attached to the 

 transN <!>. ,-i\is oi' the main telescope by means of a hub, which is screwed upon i 

 lon.u r at ion of this axis beyond the standards. The hub contains an independent hori- 

 zontal axis upon which the side-telescope may be revolved, and to which it may be 

 i-lamped. The side-telescope is usually set parallel to the main telescope, and look- 

 ing in the same direction, but it may be set so that it is inclined at a given vertical 

 anglo when the main telescope is horizontal. A counterpoise is attached to the other 

 end of the transverse axis of the main telescope, so as to balance the weight of the 

 side-telescope and retain that axis horizontal when the side-telescope is in use. The 

 side-telescope is mainly intended as an auxiliary in measuring vertical angles, and it 

 is on this account that the simple meansof attaching it to the transit, here described, 

 has been adopted by us as sufficient for the purpose, although it will be very difii- 

 cult to place its line of collimation truly parallel to the main telescope for all focus- 

 sing positions of the object-slide. When greater accuracy and greater permanency 

 in the adjustments are desired, our Universal Mining Transit No. 8, page IT-J, 

 should be chosen. This has duplex telescope bearings, one set of bearings being 

 placed excentrically, so as to permit of vertical sighting up or down a shaft with the 

 main telescope alone. 



The adjustments of the detachable side-telescope are as follows : 



1. To place its vertical wire perpendicular to the transverse axis of the instru- 

 ment. Attach the side-telescope and the counterpoise to the transverse axis. 

 Clamp the side-telescope slightly to its hub, bisect a point by its vertical wire and 

 move the main telescope on its horizontal axis of revolution. If the point remains 

 bisected by the vertical wire of the side-telescope throughout its entire length this 

 adjustment is correct. If not, loosen the capstan-headed screws and rotate the 

 reticule bearing the wires, as explained on page 48, until the wire bisects the point 

 throughout its entire length. Then slightly tighten the capstan-headed screws as 

 explained in " Some Kemarks Concerning Instrument Adjustments," page 24. Also 

 see footnote on page 49. 



2. To place the intersection of the cross-wires of the side-telescope in its line 

 of collimation. This may be done in several ways. 



(a) The side-telescope being detachable, it could be adjusted by rotating it in 

 wyes, were any at hand. Such wyes, as we have shown before, may be impro- 

 vised by cutting the proper shapes out of thin wood, and fastening a pair of them 

 to a board in an upright position. The distance between them should be such that 

 the telescope may rest upon the outside of the mounting of the object-glass and 

 against its shoulder where the cap is placed, and upon the tube near the cross- 

 wires when practicable. The improvised wyes being placed on a firm support 

 and fastened so that they will not move, the side-telescope may be revolved in 

 them, and the wires may be placed in the line of collimation as in a wye-level, using 

 a distant point. The horizontal wire, being the more important one in the side- 

 telescope, should be placed with some care. 



(b) This adjustment for collimation may be made without removing the side- 

 belescope, if for the adjustment of the horizontal wire, a small spirit-level* mounted 

 on a metal base, similar to those described on page 127, is at hand. Then proceed 

 thus: 



Adjustment of the horizontal wire, First, level up the instrument by its plate 

 levels. Then, placing the main telescope in a horizontal position by its level, 

 ihi'l a well-deiined object, such as the target of a leveling rod, distant about 300 feet. 

 Now clamp the side-telescope when in a nearly horizontal position to its hub, and 

 placing the auxiliary level, which has been previously adjusted, longitudinally on 

 the side-telescope bring its bubble to the center of the tube by means of the tan- 



* Such a spirit-level mounted in a cast-iron frame, and good enough for this purpose if carefully selected, 

 can be bought in any of the better equipped hardware stores. 



