The Story of Television, a 1956 documentary from RCA, traces the evolution of the medium from its inception to the development of color television. The film features David Sarnoff, RCA's Chairman, and Vladimir Zworykin, an inventor and pioneer of early television technology, delivering a few awkward lines about their research and development, interspersed with some fascinating archival footage of early NBC studios and equipment. 

Courtesy of the Prelinger Archive, the full 26-minute film is a little slow but the excerpt below includes an interesting explanation of how black and white television works and a look at television's growing role in American society in the late 1930s and 1940s. The narrator gushes at every groundbreaking development: 

In 1937, television strode out of the studio with mobile vans developed by RCA and NBC -- versatile, self-sustaining. New eyes, new vision for the world! A man could sit at home, yet his eyes could scan the countryside. A bright new era dawning! A new dimension in communications! Distance reduced to microwaves! Walls, barriers, mountains earased! Television: the ultimate triumph in man's search for sight beyond the range of the human eye!

For more from the Prelinger Archive, visit http://archive.org/details/prelinger.