The so-called "bouncing ball" was a device used in the early motion picture industry to visually indicate the rhythm of a song, the singing of which was typically led by the theatre's pipe organ.
Beginning in the 1920's many American theatres, during intermissions or weekend matinees, would conduct sing-a-longs involving audience participation, and, at these times, when the theatre management wanted to present an old or new song to the audience the organ would play while the song's lyrics would be displayed on the bottom third of the screen.
An animated bouncing ball was projected onto the screen to land on each syllable of the song as it was being sung (photo).
This ball would "bob" up and down, left to right, on each syllable to keep the audience singing in unison while the organ would be setting the tempo, establishing the key, and "drumming" the tune, the whole tune, and nothing but the tune into the listeners ears.
This innovation of "follow-the-bouncing-ball" was invented in 1924 by animation pioneer Max Fleischer and first introduced for the "Ko-Ko Song Car-Tunes"; it was later revised when the "Screen Song" series started out in 1929 and ran through 1938; many of these Screen Songs were planned as promotions for live theatrical appearances by celebrities of Broadway, radio, and recordings, all part of a new marketing plan launched by Paramount for the 1930-1931 theatrical season; the Screen Song series developed into a popular attraction and lasted right through 1938.
Anyone back in the day who had a dime to go to the Saturday matinee would be exposed to these sing-a-longs; before the usual serial and western a cartoon would play that featured popular songs; mice and pigs would strike up the band as the lyrics scrolled across the bottom of the screen; a bouncing ball would land on top of them at the appropriate time to keep everyone singing together.
People ate it up; they sang their hearts out; if they went to the movies often enough, they could sing their way through the Great Depression.
Only a very few were indifferent toward it or claimed they hated it; watching the bouncing ball evidently made them feel manipulated and used -- indeed, during the difficult years of the 1930's some may have felt they had little or nothing to sing about; the vast majority of the public however welcomed the lift it gave their spirits.
This type of activity, obviously, could never compete in today's world with television and the 60-second average attention span of the modern theatrical audience, but back then it held a firm place in American musical culture in the way people were entertained in that time.
The type of songs chosen for these sing-a-longs often involved a medley of three or more numbers of an upbeat nature, and, at times, a slower tune or two also could be thrown in, particularly if it was something new the management was interested in getting before the public.
Naturally therefore, the style of playing used by the organist to lead these sing-a-longs had to emphasize the top line, either with something near a full organ for the upbeat tunes or with Voxes and Tibias for the slower numbers, but always with heavy emphasis on the melody.
Few realize that this required a deliberate strategy on the part of the organist -- a definite approach to playing this music settled upon in advance for the sake of uniformity, leaving nothing to chance.
In terms of technique this translated into the employment of 1) "left hand melody" for the louder upbeat tunes, and 2) chordal playing with a liberal use of two-handed chromatic glissandos connecting any wide upward leaps in the melody against a very abbreviated and simplified left hand accompaniment for the less-assertive lyrical numbers.
These two forms of expression required separate practice to perfect but eventually became habitual.
NOTE: Some organists preferred to execute these ascending chromatic glissandos always in close harmony with the hands a minor 6th apart, and they rather deliberately avoided the use of open harmony; this can be tricky at times because, depending upon the starting chord, the left hand might have to be started a little early or later so that it came out even with the right hand at the top of the chromatic "climb," and still land on the destination chord in consonant harmony without disturbing the rhythm; with left hand melody it wasn't quite so problematic; the left hand simply played the tune legato in the tenor range of the Accompaniment manual in single notes with 8' and 4' stops drawn while the right hand played the tune marcato in big 4- and 5-note chords animated with a rhythmic pattern in the middle/upper ranges of the Great manual using something at or near the full organ with the 16' Tuba included in the Pedal; the number of notes in these right hand chords were always the maximum possible.
Musicians seem to learn quickly how to select and adapt a technique to the shape and nature of a melody and just as quickly come to realize that trying to make a "one-size-fits-all" technique work with every melody places them at a serious disadvantage; even so, theatre/cinema organists of that day had their own preferences, and they stuck with them -- but whatever approach they took for leading these sing-a-longs it was in sharp distinction to those wonderfully dramatic and extended song arrangements characterized by wide dynamic variations, creative introductions and endings, multiple choruses, segues (modulating bridge sections) between choruses, and bravura passages which truly displays the imagination and musicianship of the organist, launches careers, and builds reputations.
Appropriately, the terms some organists have adopted to describe this highly specialized manner of using the theatre/cinema organ are "Bouncing Ball" style, "Sing-A-Long" style, or, more commonly, "Old Theatre" style, and it's flat-out gripping and captivating to hear when skillfully performed on the right kind of instrument (it's also best illustrated with examples, and a YouTube video is being planned).
It's interesting that, with the more recent introduction of screens into the worship service. the tech teams at various churches, in an attempt to solve the problem of congregants singing lyrics either too soon or too late, have introduced a ball that bounces on the correct lyric at the appropriate time.
This digitally imposed ball bounces on each word at the exact moment the worship leader sings it, allowing churchgoers to actually follow along; it runs on proprietary software that tracks the worship leader's words in real time.
Those enamored with this high-tech version of Max Fleischer's original invention expect it to greatly reduce the incidence of any embarrassing outbursts of the entirely wrong verse during congregational singing for those worship services employing praise bands.