HOW TO WORK. 



How to Set Up the Instrument. Draw the 

 instrument from the case by grasping the base and 

 pillar, free it from dust with a large camel's hair brush 

 i inch or i 1-2 inch wide or by wiping carefully with 

 a chamois skin or old linen handkerchief. Place the 

 instrument on the work table, which should be of such 

 height that observations can be made with the utmost 

 possible comfort without straining the neck or com- 

 pressing the chest. Bear in mind always to sit as 

 upright as possible. 



If the instrument is used in the upright position, 

 place the base close to the edge of the table; if 

 inclined, it may set farther in. Rest the arms, as 

 much as the height of the instrument will permit, upon 

 the table. 



Bring the tube to the standard length for which the 

 objectives are corrected. To do this grasp the milled 

 edge of the draw-tube and give it a spiral motion while 

 holding the main tube with the other hand, page 50. 

 There is an objection, however, that in any but cloth- 

 lined sheaths the polished tube will soon be scratched, 



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