412 



WRIGHT AND HOSTETTER: CRYSTAL GROWTH 



the crystal, provided of course the thickness of the layer tra- 

 versed by the light waves remains constant. The path differ- 

 ence can be measured by a compensator of the Babinet, the grad- 

 uated quartz, or the biquartz 20 type. 



Fig. 1. Diagram showing arrangement used in the study of crystal growth un- 

 der load. The crystal D is placed in its supersaturated solution in the tank C 

 which has parallel plate glass sides. Load is applied to the crystal through a 

 block on which the point of the loading apparatus E presses. Increased load is 

 obtained by adding weights on the scale pan of E. A beam of parallel plane po- 

 larized light from the light source A is sent through the crystal into a low power 

 microscope consisting of an objective F, a quartz compensator G, a positive eye- 

 piece H, and an analyzing prism M. 



The method actually adopted for the observation of the grow- 

 ing crystals is shown in Fig. 1 in which A is the source of light, 

 B a condenser lens, N a polarizing prism, C a receptacle with 

 plane parallel plate glass sides, D the loaded crystal, E the ap- 



20 Am. Journ. Sci., (4) 26: 370-371. 1908; Carnegie Institution of Washington, 

 Publication 158, 134-135. 1911. 



