1'OLDING FILTERS 



157 



4. The semicircle now appears as in figure 100, a, the 

 dark lines indicating the creases already formed. 



5. Fold the point i over to the point 3, and la to 3a, 

 to form the creases 4 and 40, indicated in the diagram 

 by the light lines. Fold point i over to 3 a, and ia to 3, 

 to form the creases 5 and 5 a. 



6. Thus far the creases have all been made on the 

 same side of the paper. Now subdivide each of the 



FIG. 100. Filter folding: a, Filter folded in half, showing creases; &, 

 appearance of filter on completion of folding; c, filter opened out ready for 

 use. 



eight sectors by a crease through its centre on the op- 

 posite side of the paper, indicated by the faint broken 

 lines in the diagram. Fold up the filter gradually as 

 each crease is made, and when finished the filter has 

 assumed the shape of a wedge, as in figure 100, b. 



