the Axis of a Transit Instrument. 



285 



C is an achromatic telescope fitted up with adjustable cross 

 lines placed at the sidereal focus. It rests within the Ys 

 of the support D, or those of the support E, according as it 



N 



^s 



is required to look with it through the object-glass A or B. 

 {A vertical slip of thin mother-of-pearl, having a well-defined 

 dot about the middle, would be better than cross-lines.) 



The wires of the telescope C, and those within the axis of 

 the uauiit, will require no other illumination than what is de- 

 rived 



