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.