Details and Comments

Tolkien started working on the "The Book of Lost Tales" in 1916-17 during the First War, when he was 25 years old, but he left it incomplete several years later. Those writings - though very early and called provisional, however seem to be the only place where a very detailed description of the airs around the new world is given.

From Appendix: Names in the Lost tales - Part I:

“Vilna - In QL the root VILI (without meaning given) has derivatives Vilna (changed later to Vilya) lower air, Vilmar dwelling of Manwë- the upper airs (but not ilu)', vilin airy, breezy, vílë gentle breeze. The words but not ilu refer to the definition of ilu in the sense of Ilwë, the middle air among the stars (see Ilwë). Manwë's dwelling Vilmar is not named elsewhere.

The Gnomish names for the lowest air were Gwilfa or Fâ- the latter is said to be of unknown etymology. The corresponding Qenya names are given in GL as Fâ and Favilna, and these appear in QL under a root FAGA without translation, merely as equivalents of Vilna. Other Gnomish words are gwil- sail, float, fly; gwilith - breeze, gwilbrin butterfly: these correspond to words in QL under a root GWILI, wili - sail, float, fly, wilin 'bird', wilwarin 'butterfly'. Another name of Manweg as Lord of the Winds, Famfir, is given in GL.''