The Striding Level 



This acce ..', liable in serin ing and maintaining ideal 



conditions in the tel- In many theodolites the standard- 



have been made so low, in tavor of stability, that the telescope 

 could not be reversed in altitude except by removing it temporarily 

 from its bearings and replacing it either in an opposite or inverted 

 position. For this purpose the telescope bearings must be open 

 and easily accessible, not only for the ready application of the 

 striding level to the pivots but for the purpose of collimation and 

 centering tests just explained. 



The axis hubs must be perfect cylinders and of equal diameter 

 or the line of sight will describe curves in altitude. One of the 

 important uses of the striding level is to test this equality of bear- 

 ings precisely as described foi collar disparity in wye levels on p. 14. 

 Recesses, indentations or saw-tooth ridges in the axis bearings, 

 such as have been utilized to give increased stability to an im- 

 perfectly designed standard, would not be permissible for this work. 

 In such bearings there are multiple surfaces and seatings to recon- 

 cile. The astronomer or geodecist would not utilize such telescope 

 bearings because he knows that the cylindrical hub is the only one 

 in which friction is minimized and the only one that will remain 

 in adjustment with any persistency. (See p. 77.) 



Adjustment 



It must be assumed that the telescope hubs are perfect cylinder* 

 and that the contact points of the V-notches will always find a seat- 

 ing at the same place. With the telescope horizontal, open the 

 bearings and place striding level on the pivots; center bubble with 

 leveling base, then pick up striding level and turn end-tor-end. If 

 the bubble does not remain centered, correct half of the error in 

 the leveling base and the other half with the adjusting screws of 

 the vial tube. Reverse again and, if there continues to be a slight 

 deviation, correct half errors as before and repeat until no divergence 

 exists. 



In reality, this process adjusts the bubble axis to parallelism 

 with the contact point of the notches, and incidently it brings the 

 contact surfaces of the telescope axis into a truly hori/ontal position; 

 but there is no assurance yet that it will remain horizontal when 

 reversed on the vertical axis. 



To Adjust the Telescope Axis, theiefore, swing the in 

 strument 180 on the vertical axis. If the bubble runs off center, 

 o.riect half the error with the leveling screws and the other half in 

 the adjustable bearing block in one of the journals. Swing 

 180 and continue to rectify discrepancies by this means until the 



