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SUMMARY OF CURRENT RESEARCHES RELATING TO 



plate in the manner shown at K, a number of holes being provided for 

 this purpose at convenient positions. The object-glasses of the tele- 

 scope and collimator are 7 in. in diameter and about 4 in. focal length. 

 Their tnbes are carried by collars provided with adjusting screws. An 

 additional lens of 2|-in. focus is hinged over the object-glass of the 

 telescope to convert it into a Microscope of low power, with which the 

 crystal can be directly examined. The telescope and collimator can be 

 placed at any convenient angle to one another, and the Microscope B is 



Fig. 31. 



arranged so that its optic axis bisects the angle between them. The 

 Microscope tube, which is 8 in. long, is moved by a rack-and-pinion 

 coarse-adjustment. At the nose-piece end it carries the tube-fitting of 

 a centering objective-changer, which enables different objectives to be 

 rapidly slipped into position. At the other end of the Microscope a 

 rotating analyzer N slips over the cross-webbed ocular ; this latter and 

 the prism-holder are slotted to admit of the insertion of a quartz wedge, 

 mica plate, or other compensator. A Bertrand lens L slides in the body 

 of the Microscope. 



An adjustable table T, which can be levelled by the screw W, is 

 carried by a steel rod, which can be clamped by the screw Q ; a loose 

 ...liar, clamped to the rod by a screw, enables the table to be rotated 

 when supported at any convenient height. On this table can be placed 



