6 Lees, On the Superposing of Two Cross-line Screens 



surrounded by semi-transparent bands or sides. Obviously as 



diminishes towards zero, the side p.^ of these squares increases 



indefinitely, and this is the source of the practical trouble referred to 

 towards the end of |:^2. 



Fig. 2a. 



§7. We have next to discuss the results F, of operation (m) of 

 §3, i.e., the effect of superposing sets of bands A', and ¥,. The 

 problem is clearly the same as that discussed in iii^4 ^.nd 5, except 



