ADJUSTMENTS 



In the process of adjustment six elements of construction should 

 be considered. These include: 



1. The line of sight, which passes through the intersection of 

 the cross wires, whatever their position in the tube, and the nodal 

 point in the objective. 



2. The line of collimation, which is the final position of the 

 sight line when adjusted to coincidence with the optical axis of the 

 objective. 



3. The collar axis, which is the geometrical axis of the tube. 



4. The bubble axis, which is a line, tangent to the curved sur- 

 face of the vial at the center of its scale. 



5. The wye axes, which are elements in the imaginary cylinder 

 determined by the bearing points, or pivots. Its position is deter- 

 mined by the relative height of the wyes above the base bar. 



6. The vertical axis of revolution, which passes through the 

 spindle. 



The Collimation Adjustment is intended to bring the hori- 

 zontal cross-wire into the equator of the field of view or, as noted 

 above, to arrange the line of sight so that it will pass normally 

 through the optical axis of the objective. 



To perform this operation it is not necessary that the telescope 

 shall be perfectly horizontal. The test could be conducted in two 

 V-notches cut in a cigar box, or by any other such expedient. 



Set up the instrument firmly, open the clips, sight some distant 

 object, and suppose, as in Fig. 2, the original position of the line 

 of sight to be indicated by the finely 

 dotted lines. Revolve the telescope 

 carefully in the wyes half way round 

 and let the second position of the 

 cross wires be indicated by the heavier 

 doited lines. In effect, the tropics 

 have been located and the equatorial 

 line, mid-way between them, will be 

 the position sought. 



Move the horizontal hair into the 

 equator of the field by turning the 

 upper and lower diaphragm studs in the same direction, first by 

 slightly loosening the one, then by tightening the other. When 

 the correct position has been secured, the horizontal wire will con- 

 tinue to cut the same point when the telescope is revolved on its 

 own axis. 



Fig. 2 



