36 



WRIGHT: A NEW CRYSTAL-GRINDING GONIOMETER 



Goldschmidt two-circle type is the latest and best in principle. 

 The present instrument is also based on the theodolite principle, 

 but it is essentially different in design and construction from its 

 predecessors; certain features of the Goldschmidt design have, how- 

 ever, been incorporated in it. With the new grinding goniometer 

 crystal faces can be ground with a precision of 1' or greater, and flat 

 within a wave length of light; plane-parallel crystal plates can 



Fig. 2 



also be ground normal to any given optical direction, as an ellip- 

 soidal axis {a, iS, or y) or an optic axis. The instrument has 

 been in use for over half a year and has proved so satisfactory 

 in routine work that a brief description may be of interest. 



The grinding goniometer was designed and constructed^ with 

 special reference to adjustment facilities and to precision. All 

 of the working parts are heavy and all bearing surfaces are wide 



2 The instrument was built in the instrument shop of this Laboratory by Mr. 

 J. Jost, to whose skill and ingenuity much of its success is due. The writer is 

 also indebted to Dr. C. N. Fenner and Mr. J. H. Snapp for a thorough test of the 

 grinding and polishing devices and materials which are used on the goniometer. 



