94 



SCIENCE PROGRESS 



Keeping the bottom of the stencil horizontal, and placing 

 the left-hand top cell (indicated by the dark band) on which- 

 ever of the two numbers 13 in Key-Table I. does not involve the 

 stencil travelling off the Table, we read, from left to right as 

 indicated by the arrow : 



Next, turning the stencil so that its bottom occupies a 

 vertical position on the right, we read : 



Similarly, turning the bottom to the left, we have : 



and, finally, turning the stencil upside-down, we get : 



