I was compelled to Google "circus organ" after thinking that one never sounded so nice as it does in the opening notes of this song. And I found some really cool pictures:
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This type of organ – called a calliope – was wheeled around by traveling circuses in the late 1800s. They work via steam (what?) passing through pipes (what??). Here is an old ad for one from 1874:
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The calliope is kind of distant cousins with the train whistle (which makes sense now, steam and all).
Calliope mechanics evolved a bit over time: First they were played via a series of pins on a metal cylinder (like in a music box). Then there were organ keys, and a person played them (like in that ad, above). Then things went back to rotation-based systems with rolls of paper, and resembled player pianos.
I suppose I've only heard "good" versions of what a calliope sounds like, because apparently it's impossible to keep in tune, can be heard from a mile away (no volume control), and the notes' sound depends on how hot the steam is.
Here's a video of a riverboat calliope; you can see the steam flying out of the pipes:
EDIT: I just received an email from Zachary saying that he played this very calliope on the Delta Queen in the 1980s, "When I was about 5 while traveling down the Mississippi River on a riverboat trip that included a visit to the real setting of Mark Twain's work." Amazing.
And here's a video that came up when I searched "circus organ" on YouTube. The sound is different from a calliope, but I wonder if the vast world of 1800s organs gets mixed up easily since it still came up in search results. A quick Wikipedia search helped me figure out that this is a fairground organ, which is (it turns out) different. These were found around fairs and amusement parks, and if you play this video with your eyes closed, it will make perfect sense. Though, don't listen to this if you're not in a good mood, because you will want to throw your shoe out a window.
Randomly falling into a rabbit hole like this one at 1am makes me realize how many other insane things I don't know about yet. Jeez. I could easily spend another 2 hours researching different types of organs from the mid- to late-1800s (there are dance organs and street organs too; which of these sounds the most like a baseball game?).
