190 PHOTOMICROGRAPHY 



unless panchromatic plates are used, without which the 

 differentiation of yellows and reds is impossible. Long 

 exposures are necessary with radiants of low intensity, 

 but a few seconds are adequate with lime- or arc -light. 

 The colour plates, of course, require considerably longer 

 exposure. The particulars accompanying the plates give 

 sufficient indication of the exposures and adjustments 

 required. 



