Pratt, Fletcher <br/><br/>
Secret and urgent:  the story of codes and ciphers/ 
Fletcher Pratt 
 - London:  Robert Hale,  1939 
 - 282 p.;  23 cm. 
<br/><br/> Includes index 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Cryptography<br/>Sings and symbols<br/>Symbolism
<br/><br/><label>Dewey Class. No.: </label>652.809