MICROMETRY AND THE CAMERA LUCIDA. 57 
4. Determination of the Magnification of the Micro- 
scope.—If the image of a stage micrometer be projected 
upon paper and drawn in pencil, it will obviously be 
possible, by comparing the actual size of the drawing 
with the known dimensions of the micrometer scale, to 
measure the magnification effected by the microscope. 
The size of the picture will, however, vary with the dis- 
tances between the paper and the camera lucida, and it 
is necessary to adopt for this distance a standard value, 
generally 250 mm. 
REFERENCES. 
CaRPENTER, W. B., and DaALLINcER W. H. The Microscope 
and its Revelations. London, rgor. 
Gace, S. H. The Microscope. Ithaca, N. Y., 1904. 
