CH. 77] 



LIGHTING AND FOCUSING 



35 



object. (See \ 24, 29. ) If too thick covers are used it may be impossible to get 

 an objective near enough an object to get it in focus. For objects that admit of 

 examination with high powers it is always better to use thin covers. 



LIGHTING WITH DAYLIGHT 



\ 62. Unmodified sunlight should not be employed except in special cases. 

 North light is best and most uniform. When the sky is covered with white clouds 

 the light is most favorable. To avoid the shadows produced by the hands in 

 manipulating the mirror, etc. , it is better to face the light ; but to protect the 

 eyes and to shade the stage of the microscope some kind of screen should be 

 used. The one figured in (Fig. 62) is cheap and efficient. If one dislikes to face 

 the window or lamp it is better to sit so that the light will come from the left as in 

 reading. 



It is of the greatest importance and advantage for one who is to use the 

 microscope for serious work that he should comprehend and appreciate thoroughly 

 the various methods of illumination, and the special appearances due to different 

 kinds of illumination. 



Depending on -whether the light illuminating an object traverses the object or 

 is reflected upon it, and also whether the object is symmetricallj* lighted, or 

 lighted more on one side than the other, light used in microscopy is designated as 

 reflected and transmitted, axial and oblique. 



39 

 FIGS. 39-40. For full explanation see Figs. 22 and 23. 



\ 63. Reflected, Incident or Direct Light. By this is meant light reflected 

 upon the object in some way and then irregularly reflected from the object to the 

 microscope. By this kind of light objects are ordinarily seen by the unaided eye, 

 and the objects are mostly opaque. In Vertebrate Histology, reflected light is but 



