166 



L. H. Martin 



The crystal can be brought into the vertical by adjustments of the 

 hexagonal nuts N , N , N , B rests on three ball bearings, two of which 

 move in a V groove, and the third on a flat; the crystal being moved 

 along these, by means of a fine thread screw engaging the carrier B. 



Fig. 1 (a) 



Fig. 1 (b) 



Fig. 1 (b) is a diagramatic representation of the disposition of the 

 apparatus. The tube slit S^, which serves as a fine linear source of 

 X-rays was usually .06 mm. wide. The second slit S^, serves to limit 

 the angular width of the incident beam. The edges of this slit move 

 in parallel grooves and were arranged parallel to S^, and symmetrical 



about S , by an optical method. 



