HOW. TO USE THE MICROSCOPE 27 



sunlight is obtained, it will be found suitable for microscopic 

 work. In no case should direct sunlight be used, because it 

 will be found blinding in its effects upon the eyes. Natural 

 illumination diffused sunlight varies so greatly during the 

 different months of the year, and even during different periods 

 of the day, that individual workers are resorting more and more 

 to artificial illumination. The particular advantage of such 

 illumination is due to the fact that its quality and intensity 

 are uniform at all times. There are many ways of securing 

 such artificial illumination, no one of which has any particular 

 advantage over the other. Some workers use an ordinary gas 

 or electric light with a color screen placed in the sub-stage 

 below the iris diaphragm. In other cases a globe filled with a 

 weak solution of copper sulphate is placed in such a way be- 

 tween the source of light and the microscope that the light is 



FIG. 30. Micro Lamp 



focused on the mirror. Modern mechanical ingenuity has de- 

 vised, however, a number of more convenient micro lamps 

 (Fig. 30). These lamps are a combination of light and screen. 

 In some forms a number of different screens come with each 

 lamp, so that it is possible to obtain white-, blue-, or dark-ground 



