182 USE or THE MICROSCOPE. 



compound body, and an object-glass screwed into the other, 

 should now for most purposes be inclined to such an angle as 

 will bring the top of the eye-piece opposite the eye of the ob- 

 server when sitting in the most easy posture. The next step 

 is the adjustment of the light. 



Adjustment of the Light. — If it be required to examine a 

 transparent object by day, the light must be taken from a 

 window as free from bars as possible ; but if at night, then 

 one of the Uluminators, previously described, must be brought 

 within a moderate distance of the mirror; this last is to 

 be turned about, until the light reflected from its surface is 

 seen to pass through the hole in the stage, and to fall in the 

 direction of the axis of the instrument upon the end of the 

 object-glass; then, by applying the eye to the eye-piece, and 

 moving the mirror very slightly one way or the other, the 

 maximum of light will be obtained. If the object to be exa- 

 mined be opaque, and if the Lieberkuhn, fig. 77, is to be em- 

 ployed, the lamp may be placed in the same position as for a 

 transparent object, but if required to be illuminated by either 

 of the condensing lenses represented at page 122, then the 

 lamp must be brought nearer to the observer, and the light 

 thrown upon the object by the condenser, in the manner pre- 

 sently to, be shown by diagrams. As a general rule, it is best 

 to use the low powers first, as a good light and greater clear- 

 ness of definition, together with a large field of view, will be 

 obtained ; the higher powers may be employed when the 

 observer has a good general idea of the arrangement of the 

 several parts. 



Transparent Objects. — These, previous to being examined, 

 are to be placed either with or without water upon a slip of 

 glass, and covered with a piece of thin glass or mica, or, if re- 

 quired, either of the animalcule cages or compressors, described 

 at page 130, may be employed for the same purpose. Between 

 which ever of these pieces of apparatus the object is con- 

 tained, the next proceeding is to place it upon the object-plate 

 of the stage, and adjust the latter (either by sliding it up or 

 down, or by acting on it by the stage movements), so that the 

 object, if visible to the naked eye, may be brought as near to 



