Referencing Raphael Astarita [http://www.pulpartists.com/Astarita.html] I came across this.
(During the second half of the 1950s Astarita contributed illustrations to a juvenile reference work, The Picture World Encyclopedia, published by the F. M. Charlton Company. According to advertising, this was the "first truly modern picture book encyclopedia specially written for children 6 to 16 and offered at fifty cents for each of the 12 volumes. There's never been an encyclopedia so easy to understand, so thrillingly presented, so up-to-the-minute with the very latest facts! No long wordy explanations. No dull, confusing language. The Picture World Encyclopedia informs in a bright, lively way. Every subject is illustrated in full color, with over 6,000 pictures in all!" This ambitious project took five years to complete and included illustrations by many artists, such as Paul Jepsen, Gene Fawcette, Robert Jenney, Ric Estrada, and Bob Powell.)
Is this out of copyright and if so, is it available? it would be quite a find.