MICROMETRY ySND 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 Dallinger W. H. The Microscope 



and its Revelations. London, 1901. 

 Gage, S. H. The Microscope. Ithaca, N. Y., 1904. 



