Click through this Scientifican American Cover Art Design archive going back to 1845.

I thought it interesting the magazine incorporated a intricate border around the cover art during WWI (below).

The border would disappear at the end of the war, replaced by open spacing around the image edges pointing to a more permeable border.

Also in the late 1920s early 30s, the design begins to lean heavily on the black and white coloring distinct to the classic 1950-1970s covers.

ca. 1930