The fourth and final installment in a ``Tetralogy of Elements'' (The Fountains of Neptune, etc.), in which novelist and illustrator Ducornet ``investigates the processes of fabulating, creating and remembering.'' Air is the element investigated in this last volume, which like its predecessors is filled with allusions, some obvious, some not; actual and imagined characters; and a story that's more a series of disparate set-pieces than a concentrated narrative. Here, Memory tells of her beautiful but mute elder sister, the eponymously named Etheria, ``a creature of light and air.'' The siblings' father is Angus Sphery, an eccentric scholar who believes that before the expulsion from Eden there existed a magical ``Primal Language spelled out phonetically by the planets'' and powerful enough ``to conjure the world of things.'' The family lives in Victorian Oxford and are befriended by Dodgson (Lewis Carroll), who is especially taken with Etheria's delicate beauty. When boorish tycoon Rudolph Tubbs falls in love with the adolescent Etheria, he presents her father with the chimera, a beautiful piece of jade--a gift that ensures the latter's consent to the marriage. The unhappy Etheria, however, soon leaves Tubbs, who then travels to Egypt with a mad architect and a circus performer who lives on air. Pyramids collapse, mummies turn into fertilizer, and Memory adds her own random insights, naturally about memory, which ``is like a jade cabinet...where the jade appears to be the same yet the mind is forever replacing it.'' An interesting thought, but not really relevant to the vanished Etheria, who, departing from her father's belief that language could unify all, has concluded the opposite. Rumored to be a magician, she's found ``the Word, surely a silent one,'' that can make everything disappear. Imaginative and beautifully crafted but crushed by recondite intellectual intentions. Too clever by half.