04 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 106. 



ment, and by it objects can be seen in their natural position. 

 A cap is adapted to the object-end of the telescope, to 

 screen the glass from the rays of the sun, or from the rain : 

 when the cap is used, it should be drawn forwards as much 

 as possible. 



* The requisite adjustments for this instrument are the 

 same as those of the Y level ; viz. that the line of collima- 

 tion and the level be parallel to each other, and that the 

 telescope be exactly perpendicular to the vertical axis ; or 

 in other words, that the spirit bubble preserve its position 

 while it is turned round horizontally on the staff-head. The 

 adjustment of the level is effected by correcting half the 

 observed error by the capstan-screws, e, f, which attach the 

 telescope to the horizontal bar, and the other half by the 



