Stereoviews, explained well here, drove most of the card market for 50+ years (1860s-1920s), pushing the bounds for what viewers expected from photography and paper collectibles. They proved so popular, many modern antique stores contain stacks of surviving images, with singles running a few dollars. Three of them caught my eye during this month's trip to Maine, starting with this new-to-me #5 of a bicyclist pausing for a smoke break.
While I couldn't find it in person, "Modern Mermaid" offers another sports subject from this series, also studio-shot like the baseball pose to make it appear she's reaching out toward you.
American Colortype printed at least one postcard series for Chicago's 1933 "A Century of Progress" expo and put themselves front and center under the title of "Color Progress."
Baseball fans should remember Chicago's 1933 expo as the debut of our modern All-Star Game and breakout year for bubblegum cards. See my profile of Goudey's All-Star premiums for a deeper dive!
Any stereoviews in your own collection? While surviving baseball examples seem few and far between, they cover almost every topic of interest in those days.