GENERAL METHOD OF OBSERVATION. 7 



is placed between the source of light and the stage, 

 and at such a distance from the latter that the light 

 may be brought to a focus upon the object. Some- 

 times a " Lieberkuhn " or concave silver reflector is 

 used for this purpose. 



These are the most important pieces of apparatus 

 required in examining microscopic bodies. But the 

 beginner will do well, if he have the achromatic con- 

 denser and the polarizing apparatus, to lay these 

 aside until he has had considerable practice in ex- 

 amining objects simply with the mirror and the lower 

 powers. 



General method of observation. In the ordinary 

 use of the microscope, the object to be examined is 

 laid upon the middle of a slide, which is placed upon 

 the stage. The object is then brought under the 

 centre of the object-glass, the mirror inclined half 

 towards the light and half towards the object, until 

 the object is seen to be illuminated, when, upon look- 

 ing through the eye-piece and adjusting the coarse 

 and fine movements, the object as it comes into focus 

 will be seen, as it were, drawn upon a white disk, 

 which is called the " field." 



When the object is wet, it cannot be viewed with- 

 out the application of a cover, because the water eva- 

 porates and condenses upon the under surface of the 

 object-glass. 



To avoid the danger of injuring the object-glass, or 

 crushing the object by lowering the body and object- 

 glass too much in adjustment to focus, the best plan 

 is to lower the body by means of the coarse move- 

 ment until the object-glass appears near the object to 

 the eye placed on one side of the stage, and then to 

 apply the eye to the eye-piece, and turn the milled 

 head so as to raise the body and object-glass until 

 the object is brought into focus. 



In the examination of an object, it is best to begin 

 with a low power, so as to obtain a view of the 



