Tesla also speculated that "gravity" was caused by flow of ether.
Scientists long believed in either because light travels in waves, and waves are not considered possible except through a medium of some kind.
Of course, when the Michelson-Morley experiment demonstrated that the earth stands still, they had to get rid of it, so they came up with absurd completely unproven theories such as the Lorentz contraction and then relativity in desperation to get rid of ether, and they presented these as fact, and built up the mythos and the legend of the fictional personality Albert Einstein.
Of course, now, their theories about gravity are so badly off that they were forced to concoct this notion of "Dark Matter".
And here in this idea of gravity, it is the flow of ether between particles which causes the variations in mass creating this "ether vacuum" pulling those objects with less mass toward it. In a way, it kind of reminds me of Einstein's absurd "space-time warping", as the density of the earth, due to ether flow, is beyond that of all things which rest on its surface, therefore pulling them downward toward it as objects would sink into a basin. At least, that's what I'm getting here from Sugenis.
In a way, this would make some sense as to why gases don't simply escape from the atmosphere, as they cannot escape the etheric flow of earth's mass versus their own mass (picturing water being continually poured into a basin, water here representing ether). But this still doesn't explain how they don't escape into the "vacuum" of space, given that the entire premise of this hypothesis is ether filling a vacuum to begin with. Unless "space" is not a vacuum at all but is instead filled with ether, which would then provide some explanation as to why the earth's atmosphere remains contained within the "basin" caused by its own ether vacuum.

And this all presupposes that the Firmament is not directly above earth's atmosphere, but is in fact the barrier which contains the entire universe; the model which Sugenis is expressing with this book.