...the invention of the dialogue balloon was a "good thing",

as ckc (not kc) noted in comments a few weeks ago. As well as balloons, there were experiments with blimps and dirigibles, though these designs were not as effective as hoped on account of the lack of movement on the page. Early cartoonists enjoyed a lot of scope for flexibility until the conventions settled down.

The woman below, from 1543, can only speak in question-mark balloons. She seems to be questioning the hegemony of the patriarchy and the automatic subjugation of women to the male gaze, which is why she has been sentenced to an unusually cruel form of execution involving a late-medieval sauerkraut slicer.

Slightly later, in an episode of the Nuremberg Chronicle, the speech from Mr Buttock-Cap at the left is coming out as an unwinding toilet roll. Mr Buttock-Cap incurred some form of toilet-related mishap every time he appeared in the strip, and soon became such a popular character that he was made the star of a strip of his own. The guy at the right is making a circular argument. Even so, he seems to be convincing the portly party in the middle.

The invention of lighter-than-air balloons came several centuries later, obviously, so they were named after speech balloons rather than the other way around. Some early accounts of Montgolfier's first vehicle call it a "lighter-than-air dialogue box" but that name did not catch on.

This led many early balloonists to the understandable error of thinking that a successful ascent required the passenger to talk a lot to keep the envelope inflated. This in turn inspired a tradition of sending passengers aloft while riding a horse, relying on the well-attested fact that people talk more and louder when they are on horseback.*

These are not Orb Abductions so do not panic.

Here in 1786, the pioneering animal activist Tessu-Brissy rescues an unwanted horse from the Lie-Big Viande factory where it was about to be veritably extracted. His balloon is shaped like that because it was sponsored by the Gouda Cheese Company.

* "In 1852, Madame Poitevin, who had made several such journeys in Paris, ascended from Cremorne Gardens, London, on horseback (as 'Europa on a bull'); but after the first journey its repetition was stopped in England by application to the police courts, as the exhibition outraged public feeling."
What more need I say?

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At Riddled Research Laboratory we are attempting to revive that early freedom in the shape and appearance of speech balloons. This political cartoon about the mining-in-National-Parks debacle would have been cogent as well as funny, but the artist went overboard and filled in the balloons above the speakers' heads, leaving no room for the words. There have been beatings.