CHAPTER VI. 



ILLUMINATION. 



ILLUMINATION ADVANTAGES OF ARTIFICIAL LIGHT 

 A SIMPLE OBJECT WITH A Low POWER 

 DIATOMS DARK GROUND EFFECTS. 



Artificial light being more constant than day- 

 light, it follows that exact exposures may be re- 

 peated without risk of failure. The landscape 

 photographer has no power to alter the prevailing 

 light and shade, whilst the photo-micrographer can 

 modify them at pleasure. But, on the other hand, 

 the latter will find difficulty in getting any contrast 

 at all when dealing with very transparent objects, 

 and it is here that his individuality will be mani- 

 fested. The iris diaphragm will sometimes be 

 needed ; at other times it may be the polariscope, 

 especially for crystals, or perhaps the colour screen 

 must be employed. Which method and which 

 colour screen will only rightly be selected after 

 experience has been gained. If the worker prepares 

 his own object, he can often stain it to bring out 

 its details. However, all these matters will have 

 to be dealt with separately. 



