The earliest books are known for their atmosphere, detail, and clear writing style. Between 1938 to 1942 futuristic gadgetry and exotic locations were introduced to the series. The world in these early books is a dark and "divided place". Police and authority figures usually come off poorly; the rich are portrayed as greedy and selfish; and racial stereotypes abound. Parents complained and a revision project was undertaken in 1959. Texts were streamlined; stereotypes eliminated; plots were rewritten, lurid elements deleted, chapters per book were reduced, slang and difficult words were deleted, and the writing style was tightened. The revised versions focused on non-stop action rather than atmosphere and suspense, and were meant for a younger audience with short attention spans. Commentators thought the originals had been "gutted".