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 A series of booklets distributed by mail order at 10¢ each or 6 for 50¢. They were issued in three groups of six, each set first advertised in the November 1929, January 1930 and June 1932 issues of Wonder Stories, respectively.  | 
  
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 --- see under Future Science Fiction.  | 
  
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 Details supplied by Steve Miller.  | 
   
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