22 ELEMENTS OF APPLIED- MICROSCOPY. 
In some micréscopes the two lenses of the eyepiece 
work together to produce the effect shown in Fig. 11. 
More commonly, however, the real inverted image is 
formed between these two lenses, and only the upper 
one forms the virtual image. In such an eyepiece, 
known as a negative or Huyghenian ocular, the lower 
or field lens really forms part of the objective system. 
REFERENCES. 
Bauscu, E. Manipulation of the Microscope. Rochester, 1901. 
CARPENTER, W. B., and DaLLIncER, W. H. The Microscope and 
its Revelations. London, rgor. 
Crark, C. H. Practical Methods in Microscopy. Boston, 1894. 
Gace, S. H. The Microscope. Ithaca, N. Y., 1904. 
Hacer, H., and Mrz, C. Das Mikroskop und seine Anwendung. 
Berlin, 1899. 
These references, and those appended to other chapters, include 
only those few books which have been found most indispensable. in 
the work of the course in Industrial Microscopy as given at the In- 
stitute of Technology. A very full bibliography of works on 
microscopy will be found in Professor Gage’s book cited above. 
