CHAPTER V. 



ILLUMINATION. 



Ordinary daylight is the cheapest; and for a great 

 many purposes the microscopist will find it amply suffi- 

 cient. It will be found a great convenience to have the 

 light enter the room considerably to the left of the 

 microscope, in which case we naturally adjust the mirror 

 with the right hand. Placing the instrument directly 

 before the window is objectionable, and such a position 

 should be avoided if possible. The quality, as well as 

 the quantity of daylight illumination will, as a matter of 

 course, vary with the particular aspect of the day. In 

 bright sunny weather the light from a white cloud, as 

 has often been recommended, is pure and pleasant to 

 work with, and can be used with tolerably high ampli- 

 fications with good success. In cloudy, rainy weather 

 it is still quite possible to work with powers up to, say 

 200 diameters. The recent introduction of the s whiff- 



c5 



ing sub-stage has worked somewhat of a revolution in 

 our own practice. For years we have steadily eschewed 

 the achromatic condenser as being a costly and incon- 

 venient affair, making more " bother" than it was worth. 

 The principal objection I had to urge against its use was 

 that it was a fixture beneath the stage, thus preventing 

 me from varying the obliquity of the illumination at 

 will, as I desired, and, as a rule, practically I got better 



183 



