For three-plus decades beginning in the early 1920s—before the mass marketing and mass popularity of television—radio was the foremost in-house leisure activity and information-gathering source for millions of Americans. Radio had a profound influence on popular culture. Not only did radio record historical events for posterity, but it forever altered the manner in which information and entertainment were disseminated to the public. Television (see entry under 1940s—TV and Radio in volume 3) captures both the eyes and the ears and tends to shut out other senses; it is called a passive medium because viewers tend to become absorbed in watching it and do little else. Radio, however, is an active medium, engaging only the sense of hearing; it allows listeners to use their imagination to conjure up a picture in their minds.

An example of an early radio. Courtesy of the Library of Congress.

The genesis...