116 



C. A. Steinheil Sohne, Mttnchen. 



terminates at the top in a brass dish provided with spherical hollow 

 seat. Upon this dish is placed a stage plate with spherical steel sole 

 plate by means of which the refracting edge of the prism may be set 

 perfectly vertical previous to adjustment for minimum deviation. 



The common center of the spherical surfaces is situated at the point of 

 intersection of the vertical axis of the instrument and the plane of the axes 

 of the telescopes. In the focus of the objective of the slit telescope, which is 

 provided with means for setting it horizontal and which by its bearings is 

 rigidly attached to one of the feet of the tripod, is placed a Vierordt's mi- 

 crometer double slit mechanism fitted with symmetrically moving platinum lips 

 (by A. Kruess, Hamburgh, German patent No. 17092). 



Fig. 24 



The sighting telescope is also adjustable in the vertical plane and is 

 fitted with ocular rack and objective similar to that of the slit telescope, of 27 

 millimeter (12"') aperture and 244 millimeter (9") focus. It is provided with mi- 

 crometer oculars fitted with adjustable diaphragm, magnifying 12. 27, 45 X 

 and may be rotated about the conical steel center by means of a gun metal 

 carrier. The latter may by means of a clamping plate be fixed to the divided 

 circle. This has a diameter of 160 millimeter (6") and is divided on silver in 

 1/6 degrees. 



The divisions read by th^ four diametrical alhidada verniers (60 parts 

 = 59 divisions of the limb) and by two adjustable microscopes to 10 angular 

 seconds. 



(Vid. ,,Handbuch der angewandten Optik" by Dr. Ad. Steinheil 

 and Dr. Ernst Voit, Leipzig, Teubner 1891.) 



