298 



CRYPTOGRAPHS AND CIPHERS 



[CH. XIV 



a card he has only to apply it in order to read the message. 

 This method was used by Richelieu. 



The use of the grille may be rendered less easy to detect 

 if it be used successively in different positions, for instance, 

 with the edges AB and GD successively put along the top of 

 the paper containing the message. Below, for instance, is a 

 message which, with the aid of the grille figured above, is at 

 once intelligible. On applying the grille to it with the line 

 AB along the top HK we get the first half of the communica- 

 tion, namely, 1000 rifles se. On applying the grille with the 



line CD along the top HK we get the rest of the message, 

 namely, nt to L to-day. The other spaces in the paper are 

 filled with non-significant letters or numerals in any way we 

 please. Of course any one using such a grille would not divide 

 the sheet of paper on which the communication was written 

 into cells, but in the figure I have done so in order to render 

 the illustration clearer. 



We can avoid the awkward expedient of having to use a 

 perforated card, which may fall into undesired hands, by 

 introducing a certain pre-arranged number of dummies or 

 non-significant letters or symbols between those which make 

 up the message. For instance, we might arrange that (say) 

 only every alternate second and third letter shall be relevant. 

 Thus the first, third, sixth, eighth, eleventh, &c, letters are those 

 that make up the message. Such a communication would be 

 two and a half times as long as the message, and this might 



