The question of “relativity” is much to the front at the present day, and the methods of viewing it may be divided, very roughly, into three classes:—

1.The relativity of space, time, motion, etc. Nothing being absolute— everything relative to something else. This view is very old (it certainly dates back as far as the time of Aristotle), and nearly everybody believes it; although there are still a few people who would like to believe in absolute motion, space, or rest. Even truth, however, is really “relative” ; and this was, apparently, Pilate's view when he scornfully asked, “What is truth?”

Gusts, says Duchêne, are more frequent when the machine is flying into the wind than with the wind, “for the simple reason that the gusts have a certain speed and the aeroplane therefore meets more of them (in the same space of time).” Elsewhere Duchêne refers to the experience of a pedestrian on a tramway route: in a given time a pedestrian meets more cars than those that overtake him.

I can see no parallel here, however, to meeting or following gusts in an aeroplane. Whether the machine is flying with the wind, or in the opposite direction to the stream of air, it has got to maintain its relative speed to the air: increase or decrease means a lift or a dip. So, as regards gusts in either case, the number met or overtaken would be the same. And it would seem that a following lull should have much the same effect on a machine as a head gust, and vice–versâ.