42 Wadsworth — Simple and Accurate Cathetometer. 



sensitive level attached to the upper end of this axis enables 

 the latter to be set accurately vertical, this adjustment being 

 made as in an ordinary cathetometer. 



The complete arrangement is shown in elevation in fig. 1 

 and in plan in fig. 2. A, fig. 1, is the mirror frame and B is 

 the level, mounted at the lower and upper end respectively of 

 the short conical axis C. The boss D in which this axis turns 



is attached by means of a geometrical clamp at E to a split 

 cap which slrps over the end of the observing telescope T and 

 is clamped thereon by means of the screw F. This much 

 really constitutes all of the essential parts of the new cathetom- 

 eter, the telescope mounting itself, consisting of the two re- 

 shaped bars K, GJ- and the adjusting screws H, I, being merely 

 accessory to the convenient adjustment of the axis C to verti- 

 cally. An ordinary open V-clamp M attached to the lower 

 bar Gr enables the whole arrangement to be clamped to any 

 convenient support ; such, for example, as the upright of a 

 heavy retort stand, or an iron wall bracket or even a stiff well- 

 secured water or gas pipe on the wall of the laboratory. If a 

 retort stand or other support with adjusting screws in its base is 

 used, the adjustable support G, K, etc., on the telescope itself 

 may be dispensed with and the clamp M attached directly to 

 the telescope tube as in Plate I, which shows the cathetometer 

 in use. 



In the use of the instrument the mirror is first adjusted until 

 it is parallel to the axis of rotation C and perpendicular to the 

 optical axis of the telescope T. These two adjustments are 

 made simultaneously in the same manner as described in a 



