1056 



EECORD OF CUKRENT RESEARCHES RELATING TO 



A A. The base (of mahogany). 



B. One of the two brackets of support. 



C. One of the two milled heads for clamping 

 the instrument at the desired inclination for use. 



D. One of the milled heads for coarse adjust- 

 ment of focns, acting upon a strong triangular - 

 bar (not seen in tlie engraving). 



E. illuminating prism. 



F. Milled ring for adjusting by hand the 

 azimuth of the prism. 



G. Slide, with rack and pinion, for adjusting 

 the distance of the prism from the object. 



H. Sector (seen also at h) on which the prism 

 Is moved by hand through any required arc con- 

 centric with the object on the stage. 



I. The stage ; i i, upper and lower milled 

 rings, which produce, on being turned by hand, 

 the slow motions, in two directions, of the object - 

 plate of the stage. 



K. iiracket-piece supporting the stage, and 

 also the plate for carrying the polarizer when 

 required. 



L. Toothed wheel with pinion and milled 

 nut for revolving the stage In azimuth. 



M. Dovetailed slide carrying both stage and 

 sector, with the illuminating prism. A screw and 

 its bent lever (the latter passing to the back of 

 the instrument) are partially seen at N ; and at 

 O is a spiral spring which keeps the slide M in 

 close contact with the screw N. The lever N is 

 equally available to either hand at the back of 

 the instrument ; P P are opposing screws which 

 serve to bring the optic axis of the body or tube 

 Q to coincide with the centre of revolution of the 

 stage, Q being purposely not screwed (as usually) 

 into the projecting arm, but held (with a suffi- 

 cient amount of lateral movement) between the 

 collars rr. 



