174 



PHOTOMICROGRAPHY 



" Ordinary " gives approximately the factor for any 

 non-colour sensitive plate of medium speed. 



The most noticeable feature is the very great advantage 

 of panchromatic plates so far as speed is concerned with 

 the yellower illuminants. The figures are only approxi- 

 mate, and vary with the particular lamp employed. 



Exposure Factor of the " M " Screens with Various 

 Illuminants. These factors refer to the panchromatic 

 " M " plates, and will, of course, not hold for orthochro- 

 matic plates or any others of different colour sensitive- 

 ness. They are given for the single screens, and for pairs 

 used together to give monochromatic bands. Their 

 spectral transmissions are given in Angstrom units. 



