The Johnson Tripod 



Fig:. 23 



It was found that the heavy 3-screw leveling mechanism, with 

 low motion screw of the Mensula Tripod, carried the refinements 

 of construction beyond the requirements for some topographic 

 mapping. The Johnson Spherical Socket, introduced in 1887, 

 provides for rapidity and sufficient accuracy in both leveling 

 and orientation. It is shown in perspective in Fig. 23 and in 

 section in Fig. 24. 



There is no tangent screw for slow motion in azimuth in thii 

 construction, for it is understood that the leverage furnished by the 

 outer edges of the planchette accomplishes all practical requirements. 



Fi<. '4 (From breed ,iJ Hosmei). 



42 



