DUST OF THE AIRWAYS.

Dunstan Times, Issue 3141, 30 October 1922, Page 2

DUST OF THE AIRWAYS.

(By Dr. E. H. Chapman.) It might reasonably be expected that tlie great airway of the world would be above such a thing as trouble from dust. Yet the same dust which 'harasses the busy housewife, and the motorist on the road, may be a far greater nuisance to the airman than to any person on the earth's surface. Certainly it is true that the higher you climb the purer is the air, but it is not the dust in the air at the level at which an airman is flying which causes trouble. It is all the dust in the air beneath him.

In the curious,effects it produces, dust may be a far greater menace to the safety of an aeroplane than it ever is to the* safety of a motor-car. Even at the greatest flying heights there are dust particles in the air. Much of this dust is volcanic dust which'has travelled perhaps for thousands of miles. Volcanoes emit enormous quantities of dust at times of eruption. For many months after the eruption of Krakatoa in 1888 the volcanic dust in the higher levels of the atmosphere caused most beautiful sunsets in England. Part of the dust in the air is swept up by the wind from the deserts and dry lands. Some of it comes from the sea* in the form of evaporated seaspray. Even pollen grains of plants are found floating in the air at high altitudes.

Dust in the air can of itself form a haze, and a dust-haze can play some very curious tricks. For example, it is by no means uncommon for an aeroplane to he clearly visible from the ground while, at the same time, the pilot can see nothing of the earth's surface beneath him. Such a state of affairs is generally caused by a thin curtain of dust-haze which lies between the aeroplane and the ground. The effect of this dust is similar to the' effect of a lace curtain over a window. Those outside the, window cannot see into the room, but those in the room can see quite clearly what is happening outside in the street. In the same way the pilot cannot see .he ground, but those on the ground can see the aeroplane. By far the most serious thing about dust in the air is that it encourages the. formation of clouds, mists, and fogs. Water-vapor condenses more readily into water-drops when the air is dust-laden.