250 



Mendenhall and Waidner — 



The glass tube carrying the quartz fiber passes through the 

 top of the instrument nearly down to the top of the coils, and 



carries at its" upper end a rack and pinion motion for raising 

 and lowering the fiber and system. By having the coil sup- 



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ports slender and out of the way, and the outer case of glass, the 

 space between the coils is well illuminated and easily visible. 



The movable coils furnish a quick means of varying the 

 sensibility ; and besides, they render the insertion of light and 



