best results, may be led to wrong conclusions, or 

 may injure the eyes. 



The mirrors of the microscope are usually plane 

 and concave. As it is clearly inconvenient or im- 

 possible to hold the microscope toward the source 

 of light, they are provided to reflect the light 

 upward to the object when this is transparent. 

 The plane mirror reflects the light in the initial 

 intensity of its source and is used with low power 

 objectives. The concave mirror concentrates the 

 rays on the object and thereby gives intensified 

 illumination and is used with medium and high 

 power objectives, except when substage condenser 

 is used, which subject is left for future considera- 

 tion. 



The sources of light are either daylight, or 

 artificial light from a lamp. In the former the 

 light from a northern sky is preferable and in the 

 latter a flat-wick oil lamp, or a Wellsbach gas- 

 flame. An ordinary gas flame should not be used 

 on account of the difficulty of obtaining equal 

 illumination and the constant flickering which is 

 very injurious. When using the flat-wick lamp 

 the narrow edge of the flame should be used, as 

 this is more intense than the broad side, as can 

 be easily determined by experiment. 



When using daylight, place the microscope as 

 near as possible directly before a window and 

 when a lamp is employed have it on the table 

 within easy reach. 



