POOR ICARUS! as we recalled yesterday, he ventured too close to the sun with his waxen flying apparatus, and as a result of the excessive heat
....with melting wax and loosened strings,
Sank hapless Icarus on his faith less wings;
Headlong he rushed through the affrighted air,
With limbs distorted and dishevelled hair.
It is likely that the natural phenomenon that allowed Icarus to arrive at such a dangerous altitude was what we nowadays would call a thermal - invisible rising currents of warm air, spreading heat upwards through the atmosphere from patches of ground that have been warmed by the sun. A volume of air resting on ground that has been heated in this way becomes warmer than its surroundings, achieves a certain buoyancy as a result, and begins to bubble upwards, rather like the bubbles often seen in boiling water.
Thermals are usually present underneath cumulus clouds which are themselves, indeed, a consequence of the ascending air - but they frequently occur well away from clouds of any sort. They tend to slope forward with the wind, increasing in diameter with height, and when a breeze is blowing they may be carried bodily downwind by the movement of the air, rather than remaining static over one spot.
These gentle updraughts are used for soaring flight by many of the larger species of birds, particularly in tropical regions, where it was noticed that very often "the bird that flutters least is longest on the wing". But apart from Icarus, it was not until 1930 that a glider pilot in America made use of thermals for gliding, circling and gaining height in places where birds were doing the same, he succeeded in flying for 33 miles under a cloudless sky - an amazing feat for that time.
Thermals occur at all times of the year, but in Ireland it is only in summer that the updraughts are strong enough to support gliders - and even - then only at the warmest times of the day. They are also an inland phenomenon; near the coast, sea breezes, which bring cooler air in from the sea, inhibit their development. Glider pilots find that the strongest lift occurs in the central core of a thermal, and to take maximum advantage of it, he or she must fly round and round near the core, gaining height all the time in an exhilarating upward spiral. Indeed it is only by taking advantage of these and other characteristics of the atmosphere, and by making use of its changing and unseen movements, that the sport of gliding becomes possible at all.