Growing.

The 1960s were a decade of change for radio. Having weathered the challenge of television in the 1950s, something that most observers said was unlikely, radio was growing as an industry in the 1960s, even if individual stations faced struggles.

New Role.

But radio was no longer the national entertainment medium it had been in the 1930s and 1940s, playing network programs of comedy, drama, information, and music. Starting in 1948 with the advent of network television, the networks transferred many of their popular radio shows and their stars over to television. Jack Benny, Lucille Ball, Amos 'n' Andy, and dozens of other stars and shows ended up on the visual medium.

Transistors.

But radio survived and even prospered. In 1949 there were 80 million radios in the United States. In 1965 there were 228 million. Most of the growth was provided by a 1948 invention at...