Rollins — Ruling Concave Gratings. 



53 



motion of the diamond should be controlled by a carriage 



moving on curved ways, that the long axis of the diamond may 



always preserve the same angle with the surface of the grating. 



For the idea of applying the curved ways to the movement of 







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the diamond I am indebted to Captain Khotinsky, whom I 

 engaged to make the drawings for a ruling machine which was 

 to embody the ideas which had occurred to me during a study 

 of my Rowland grating. 



Boston, Mass. 



