Firmament - The Layers of the Sky

Main credit goes to Geekluminati for inspiring me to add floating islands to my world and helping to explain how it's meant to 'scientifically' work.

Any pilot worth his salt these days should know about 'the eight layers of the sky', each with their own characteristics and hazards. The earliest references to those eight layers can be found in records pre-dating the year of collapse, but it wasn't until the advent of gossamer-propulsion that our own researchers had the means of testing and confirming these ancient concepts.
The first is the air directly above and around us, for about one koz directly upwards. As our engineers have found, it takes a lot of power to raise a vehicle into this type of air; with recent advances in magic and technology, we are getting closer to making such vessels more commonplace, but a lot of this is still in the experimental phases. That is, we know that to get anything of great weight into the air we need a source of propulsion, an engine of some sort, and a careful understanding of aerodynamics. Thus our best examples until recently were simple gyroplanes and gyrocopters, and even they require the aid of magic and summoned spirits to compensate for our misjudgements.
The second layer lies where the largest clouds settle, about two to three koz above us. However, as we've sadly recently discovered, these are also the most dangerous environs for airships, placing pilots straight in the path of rain, hail and lightning; to speak nothing of strong winds or other spirit-spawned disruptions. Better to seek higher altitudes, and quickly!
The third layer takes pilots beyond all but the thinnest of clouds and the so-called 'anvil heads' of towering thunder storms, at about 1 yojan directly upwards. One should still be wary of pockets of turbulence, treacherous phenomena created by the intersection of the great air-streams that gird our world, but this is where we are told most commercial and military airships travelled during the age of fire. These first three tiers make up what we call the 'nimbus layers', and so the third layer is also known as 'the cloud's reach'.
The fourth layer, also called 'the verge', is where one breaks past the highest clouds into a space where the air is thinnest, almost unbreathable. For most airships, this is not an ideal cruising altitude, and one must now keep windows and doors pressure sealed while one continues to rise. Eventually 'the aether' grows thicker, the ship becomes lighter, and airships that can get up to this level start requiring less power to keep rising. Eventually they begin to float of their own accord; without need for extra propulsion, like a barrel rising through water. Up and up...
Up to the the fifth layer, known as 'the second sea', where the aether settles out into an invisible ocean. This layer also represents the limits of what is reachable with any known technology. Just like a sea boat cannot spontaneously lift from the water into the air, a sky boat cannot seem to gain purchase whatever lies above the aether. It is here that we find a few sparse floating islands, frozen ruins, and floating wrecks from ancient battles. The aether is clear and frigid but breathable, like air. Fire will not burn in it though, so expeditions to the second sea are are perhaps the most dangerous expeditions known to man. Still not much is known, and we were foolish to go there so unprepared.
As our explorers have reported though, the fifth layer also presents us with a new challenge: The question of getting back down. We have found, for example, that birds and insects seem to occasionally get swept up into the second sea on wild air-currents, and they cannot fly back down through the verge by their own volition. It's miraculous that they even survive at all, but there are venerable denizens in the reaches of the second sea that have carved out a place for themselves in that harsh ecosystem. So back to the question: To drop back down from this sky-sea, back past the verge and into the nimbus layers again, and back to Terra-Loka: We will require any future expedition airships to be equipped with their own 'reverse propulsion' or 'anti-weight' systems; else they are trapped up there with the rest. This is a challenge we still face; and the hope is that examining some of those wrecks will hold an answer... May Akasha have mercy on their souls.
*Ahem*
The sixth layer has been referred to by our brave explorers as 'the plumes', and it seems to work similarly to our own nimbus layers: Dictating the climate on the floating lands. Here, aether winds can suddenly increase in speed, creating almost invisible whirlpools that tear things asunder. The plumes carry weather formations in them, similar to clouds, but usually only in the form of dust-storms and lightning-whirls during the day, or icy hail and thick blizzards at night. Otherwise the days on the islands are bright and hot under the cloudless black sky, and as the last night's snow melts, it collects into streams, and eventually pours back into the clouds and lands below. Buildings on the floating islands have to built differently to withstand the plumes, and plants and all living things are simply adapted differently too. Most buildings have extensive basements for living in, for example, whereas the upstairs areas are usually used for cold storage, and the roofs are for tanning during the day or freeze-drying foods at night.
We know precious little from the old grimoires, fragmented as they are, of the seventh layer. Whereas the plumes are howling deathtrap, the so-called 'gap' or 'bridge' (depending on your preferred translation) is described as a place of dreadful calm: Even the aether is too thin to breathe here, and it is likely far too cold for even the hardiest spark of life. Yet, this place is mentioned in those old texts, and frequently. One can only wonder why. Light dances here in strange patterns, forming the great Aurora-Loka that beguiles the eye and dazzles the mind: The Ring of Reincarnation, Syol themself.
The eigth layer is the firmament, of course. The ceiling of our world, it seems. Where-from the stars are hung, and the sun and moon make their daily journeys. And as for beyond…? Even the ancients were silent on that subject. Perhaps to piece the eighth layer would place you on the doorstep of Heaven itself. Artists and poets believe that, after all, that is what the stars are; like morning light shining through a window's veil.

— Excerpt from a lecture given at the Vritrian Aeronautics Academy, 413 CE

Type

Island, Floating

Location under

Bulwark, Loke - The Body of the World