ADJUSTMENTS 



The adjustments of the precise wye are more simple than the 

 ordinary type. Nothing need be seriously considered but the 

 parallelism between the collimated sight-line and the tangential axis 

 of the bubble. 



The Collimation Test is conducted as directed on page 

 6, except that a little more care and dexterity should be exercised 

 on account of the heavier telescope and the avowedly less rigid 

 structure of the base-bars. The automatic spring clips are provid- 

 ed with small spring plungers to insure a perfect seating of the 

 collars in the wyes. These should be thrown open and in turning 

 the telescope in the wyes it should not be grasped by the eyepiece 

 only, or in any other way that may induce a torsion or side pressure 

 during the process of revolution. 



An annular clamp encircles the telescope tube near the ocular. 

 This is provided with cams and adjusting screws that engage a lug 

 in the front wye so that 180 revolutions can be very exactly 

 regulated. They are to be adjusted by sighting the telescope on 

 a plumb line with the lower adjusting screw set so that the vertical 

 wire is in coincidence with the line. Revolve the telescope very 

 carefully, so as to avoid a shock when the other set-screw comes in 

 contact with the lug, and bring the vertical wire once more into 

 coincidence by the other adjusting screw. 



^COLLARS 



e 



.A 



Fig. 5 



To guard against, or to reduce the effects of lateral displace- 

 ment in the objective mount, with respect to the collar-axis, the 

 collimation adjustment should be conducted by sighting at infinity, 

 or upon some object in the distant hori/on. Otherwise a slight 

 angular error will creep in, expressed by the formula: 



in \\hich a is the amount of eccentricity ni the objective, above or 

 below the geometrical axis of the collars, and D the distance to the 

 object sighted. 



12 



