THE MICROSCOPE AND ITS PARTS. 23 



When ready to examine an object, the stand is 

 placed near the window, or, if at night, the lighted 

 lamp is stood near the instrument on the left-hand 

 side and one or two inches in front of the mirror, and 

 the objective is screwed on. The microscope is 

 inclined at a convenient angle; the mirror is moved in 

 various directions, until the light is reflected from a 

 white cloud, if possible, or from the lamp, to the front 

 of the objective, where it can be easily seen. The 

 eye is then pla'ced at the eye-piece, and if the field is 

 imperfectly lighted, as it probably will be, perhaps 

 one-half of it being in shadow, or only a faint trace of 

 light visible at one side, the mirror is slowly moved 

 until the field is brightly and evenly illuminated, when 

 every part of the circular bright space within the 

 instument is as well lighted as every other part. The 

 position of the diaphragm is then changed, to be 

 further altered, if necessary, after the object has been 

 placed on the stage. This even illumination may at 

 first be a little troublesome to obtain, but as in so 

 many other actions in connection with the microscope, 

 a very little practice will overcome every difficulty. 

 The fingers are soon taught; they speedily do their 

 work without their owner's conscious bidding. 



The specimen to be studied may be permanently 

 preserved, or "mounted," on a slip of glass, under a 

 thin cover and surrounded by Canada balsam, glycer- 

 ine, or some other preservative, thus fprming prepara- 

 tions called "slides," or "mounted slides," the plain 

 piece of glass without the object being a "slip." The 

 addition of the object therefore changes the slip into a 

 slide. It is well to remember this distinction in talk- 

 ing with the dealers or in sending orders by mail. 



