M an cJi ester Memoirs, J^o/. Ixiii. (1919) No. 4 



Plate I. 



The effect of superposing two "intaglio " screens (white lines on a Vjlack 

 ground) at an angle of 2''2''. Pitch of screen 150 lines per inch. 



Fig. 4. 

 Same screens as in Fig. 3, but angle is now 5^ 



