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ical laboratory. It is useful then to know of some substitute for 

 the regulation model, a substitute which may be constructed from 

 the usual apparatus which is found in the laboratory. Having 

 had occasion to set up a number of them, I supplemented the 

 instruments I had in the following manner. An ordinary stand, 



Fig. i. 



with a knee-joint, was inclined to the horizontal. This served as 

 the horizontal microscope itself, after all of the substage appa- 

 ratus had been removed, the front lens taken off from the No. 3 ob- 

 jective, and a micrometer ruling placed in the eye-piece. So far 

 it is very simple and the idea, at best not a very remarkable one, 

 might occur to any one. The chief difficulty, however, in con- 

 structing a horizontal microscope is to provide for the adjust- 

 ment of the object to be measured, so that it can be brought in 

 the desired position before the scale and so moreover it may be 

 changed in vertical position without any lateral disturbance. Any 



