Saelum

Saelum (/ˈsei.ˌlʌm/, occasionally /ˈʃai.ˌlʌm/ is the name of the thick gas that surrounds the flislands. Saelum has a chemical makeup startlingly similar to air, as it is made of 78.09% Nitrogen, 20.95% Oxygen, 0.93% Argon, 0.53% Tantalum Trithallide, and 0.02% Carbon Dioxide . The boundaries between true air and Saelum are blurry, as both compounds are invisible to the naked eye. However, Saelum pockets do increase at the edge of flislands, and disappear on the surface of flislands . Saelum is, at it's thickest, ten times more dense than air, though it is still breathable at this density.

The Saelum, like air, is subject to winds. These Saelic winds can be used to push sailboats, though these winds will always point north.