16 MICROSCOPY FOR BEGINNERS. 



when reversed, to be screwed to the stand. If it is not 

 to be returned to the box immediately after use, as will 

 often happen if the student has more than one, and he 

 desires to examine the object with another power, stand 

 it on its screw end on the table, and to protect it from 

 dust invert its box over it. The latter can be lifted off 

 in a moment, and the objective will then be ready to 

 be picked up as before. 



What objectives should the beginner select ? If pos- 

 sible, he should have two, a low and a moderately high 

 magnifying power. If unable to purchase both at once, 

 let him by all means first take what is called the one- 

 inch objective ; if he can also buy a high - power, the 

 or % will be the proper glass. But for this he can 

 wait. There is so much to be examined with the one- 

 inch objective that, for a long time, he will scarcely feel 

 the need of another. The inch, if properly selected, 

 need not be expensive, but it should be a good and sat- 

 isfactory glass, not only at the outset, but when the stu- 

 dent becomes an expert microscopist ; it will then always 

 be useful. Such objectives are made by several Ameri- 

 can opticians, and included in what they call their " Stu- 

 dents' Series." "When in focus, the distance between the 

 front lens and the surface of the object the "working 

 distance " is large, so there will be no trouble in using 

 it; and with the two-inch, the "A" eye-piece, the mag- 

 nifying power will be about forty-five diameters, or a 

 little more than two thousand times. 



After the student has been using the one-inch objec- 



