Fi g 42 Showing general equipment with Vertical Clamp, Telescope 



Bubble and uncovered Vertical Circle, as supplied with the No. 44 



4^4-in., No. 54 s-in. and the No. 64 6-in- Tachymeter. 



the telescope is focused on some particular object, without touching 

 the objective, for the image formed by the objective lies in the plane 

 if the cross wires and when the cross wires reappear in sharp focus 

 the image will also 6e in focus. 



We cannot furnish the variable power e epiece with a 4-in. or 

 4 '2 in. instrument. With the 5-in. instrument a range of power 

 between . . 15 and X25 is possible; with the 6-in., between X17 and 

 27; with the 16-in. wye level, between XI 3 and X26 and with the 

 21 -in. wye level, between X18 and > 36. In the last two cases 

 the cross wires reappear as the magnification is doubled. We can- 

 not supply the variable power with the inverting telescope except by 

 furnishing extra oculars of various focal lengths which are to be 

 interchanged as the conditions require. 



The New Interior Focusing System is peculiar to our 

 Tachymeters and portable Theodolities. It is the result of an 

 effort to make these instruments as nearly perfect as possible. Hu\ 

 ing given our best attention to the quality of the lenses, the ac- 

 curacy of the graduations, and the rigidity and accuracy of the 

 mechanical construction, the principal outstanding source of error 

 waa the disturbance of coLlimation adjustment in the process of 



83 



