I love that the balloons are far too small. Like they didn't understand the elements and buoyancy well enough to know the balloons have to be much larger. Not like we have negative mass particles.
I'm pretty sure scientists back then could have told you that these balloons are too small. The person(s) who drew that picture most likely wasn't a scientist, which is why it looks how it looks.
What about hydrogen plasma as hot as the surface of the sun, contained in a weightless force field? The 'balloon is simply a decorative wrapper? Remember, it's the future year 2025!
Next we'll be trying to explain why they needed a garbage disposal on the Death Star.
[Two reasons. first, the builder was trying to slow things down so he threw in extraneous stuff. second, there were regulations about ships over a certain tonnage, because no one wants tons of trash falling onto their planet.
I was thinking about this a bit yesterday and I think the most feasible way would be to suspend a glass sheet above the lake, and then give people harnesses with magnets on the top that attach to magnets on the other side of the glass sheet. Then just put ball bearings on both sides to reduce friction.