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SUMMARY OF CURRENT RESEARCHES RELATING TO 



had nothing to complain of in this respect. He also found that the 

 velocity of the carriage had no perceptible effect upon the dimensions of 

 the scratch, which, by the way, was frequently invisible to the naked eye. 

 His experience seems to warrant the conclusion that the scratch obtained 

 and measured by his method is a trustworthy indication of the hardness 

 of the material. 



Swift and Son's Stage Goniometer. — This goniometer (fig. 110), 

 which is a modified form of Professor Miers' Stage Goniometer, 



Fig. 110. 



designed by Professor H. L. Bowman, is clamped by two screws to the 

 stage of a " Dick " penological Microscope. It is fitted with complete 

 arrangements for adjusting and centring a crystal similar to those 

 employed on the large instruments. By means of these adjustments a 

 small crystal, mounted on the end of the steel pin, can be brought to 

 coincide with the turning axis, and adjusted so that one of its edges is 

 parallel to this while it remains under observation. The instrument is 

 specially designed with a view to great rigidity and delicacy of adjust- 

 ment in order to enable a crystal mounted on it to be observed under 

 high powers. It is, therefore, invaluable for the examination of minute 

 crystals, particularly such as show twin lamellation or similar complex 

 structures, in respect to etching pits and extinction angles on different 

 faces. The optic-axial angle of a bi-axial crystal or fragment can be 

 measured with absolute accuracy. The crystal can, if necessary, be 



