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CONTRIBUTIONS TO MICRO-MINERALOGY. 



its coarse rackwork adjustment R, and the secondary stage, on 

 to which fits the diaphragm, polarizer, selenite plates, &c. A 

 tube screws into the top of the bar G, on which slides the mir- 

 ror. The object-glass and stages are centered, but the mirror 

 has free motion round the supporting-rod. 



The Body sHdcs into a socket attached to the prism-box at 

 the proper angle, so that its axis shall be perpendicular to the 

 outer face of the prism P. Within the draw-tube there are 

 fittings to receive glass tubes for examining with a Leeson's 

 goniometer and minute-stop, the amount of rotation in liquids 

 that exhibit Ciicular Polarization. If in place of the long body, 

 a tube of iron, round which copper wire has been wound, be 

 used, and the ends of the wires be connected with 12 or 

 more cells of a Groves or Maynooth battery, the rotation of a 

 polarized ray may be effected. 



