When animals came out of the sea, they had to learn to breathe air. In fact, says Daedalus, they never did. They took their own water with them. Even today, we still breathe water: we absorb the oxygen which dissolves in the moist lining of our lungs.

So why can't we still breathe water? Sadly, bulk water contains too little oxygen for our modern needs — only about 0.7% by volume, compared to 21% in air. But Daedalus has a way out. Imagine, he says, a dense foam of tiny air-bubbles in water. If all the bubbles had the same diameter, and were packed closely together, they could not easily rise to the surface. The result would be a curiously viscous stable foam, analogous to those ‘rigid’ close-packed emulsions of oil in water, whose droplets can hardly move past one another.

To make this foam breathable, Daedalus will dissolve suitable salts in it, bringing it into osmotic balance with lung tissue, and will add the natural polysaccharides that give saliva and sputum their viscosity, and a detergent like the one that helps the lungs to expand. He will aerate the solution through a battery of uniform nozzles, compress it briefly to collapse bubbles smaller than the standard size, and drain it to pack the remainder tight. It will then contain 74% of air by volume, giving it a density of 0.26 g ml−1.

Daedalus's ‘Liquid Air’ will be a novel environment. You will sink into it, but will still feel somewhat buoyed up. It will be easier to move through than water, more opaque and sound-deadening than the densest fog, and rather an effort to breathe. Extra oxygen may be needed to make it feel comfortable and safe. But then the novelty of the experience, the sense of entering a silent, private fluid world, should make the Liquid Air immersion bath a popular relaxation.

Other more serious uses should also develop. With its high water content, Liquid Air will be utterly fireproof. Pumped in volume from fire-tenders, it will blanket rescuers as they enter burning buildings; injected into threatened aircraft, it will extinguish fires and blind and disorientate hijackers. Even better, bullets and explosion-fragments would be rapidly halted by Liquid Air. Pumped into and around suspicious vehicles and packages, it would damp an explosion wonderfully. The blast would expend its energy in ‘inverting’ the air-water emulsion to a dense spray of liquid droplets.