Visit a living room on a Saturday in the 1920s: What you are likely to find is family or friends gathered around the Victrola, laughing at the antics of a comedy routine recorded on a disc, or even a tube, called the 78. Technically, the 78 was produced as late as the 1950s, but the real heyday of the medium ended in the 1940s, as radio variety shows took their cue to air the popular comedians, and to add musicians and singers for variety. The performers...