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SUMMARY OF CURRENT RESEARCHES RELATING TO 



author has devised the following instrument (fig. 7), whereby with a 

 rack-work and simple link-motion, the collimator, which renders the 



Fig. 7. 



incident rays parallel, and the telescope, in which is placed the analysing 

 Nicol's prism, are simultaneously moved through equal angles. The 

 opaque body is placed on a movable table with levelling screws, which 



