168 ELEMENTS OF APPLIED MICROSCOPY. 
All these factors are of great importance in determining 
the hardness of steel; it is therefore natural that the 
microscope should have become indispensable in the 
laboratory of the iron and steel expert. Its practical 
application to the study of other alloys promises exten- 
sive development in the future. 
REFERENCES. 
Ciark, C. H. Practical Methods in Microscopy. Boston, 
1894. 
LuqueEr, L. M. Minerals in Rock Sections. New York, 1898. 
ZERKEL, F. Lehrbuch der Petrographie. Leipsic, 1893. 
RosEnsucH, H. Ippinoes, J. P. (translator). Microscopical 
Physiography of the Rock-making Minerals. New York, 
1893. 
Hiorns, A. H. Metallography. London, 1902. 
Sauveur, A. The Constitution of Steel considered as an Alloy 
of Iron and Carbon. Technology Quarterly, XI, 1898, 78. 
