65 MA G N1F1CA T1ON. 



crons, and the reduction is simply made by multiplying the actual 

 size of the object by 1-1000. 



In all measurements with the microscope, the draw tube 

 should be pulled out, until the whole tube of the microscope is of 

 a certain length. This distance is known as the "tube length" 

 and varies in microscopes of different makers, as do also the points 

 between which the measurement is made. See Prof. S. H. Gage's 

 Microscopical Methods, p. 10. 



In order that the student may become familiar with the work- 

 ing of the microscope he should carefully go through the following 

 exercises: 



1. Putting the ocular and objective in position, p. 57. 



2. Lighting the field of the microscope, with direct and 

 oblique light, p. 62. 



3. Determine the relative position of optical sections, and the 

 manipulation of the fine and course adjustments, p. 61. 



4. Study of ail- bubbles and oil globules with reference to the 

 identifying of each by their appearance, under direct and oblique 

 illumination, p. 62. 



5. Study of currents in liquids and their direction upon incli- 

 nation of the stage of the microscope. These currents can be 

 produced by grinding upon a slide, with a knife, a little carmine in 

 water, and covering with a cover glass. 



6. Determine the magnification of the instrument with the 

 various combination of lenses, p. 63-64. 



7. Dirt or cloudiness on the lenses, p. 60. Smear the objec- 

 tive with glycerin and study the appearance. Remove the glycerin 

 with water. 



8. Mount various objects (hair, cotton and woolen fabrics, 

 bits of wood, paper, thread, etc.), under a cover-glass in water, and 

 study with the high and low power. In this way one will become 

 familiar with the adjustments of the instrument and the appear- 

 ance of the more common "foreign bodies" that might be found in 

 ordinary preparations. 



