By means of data collected from numerous sources relative to meteorological phenomena observed in flying, an attempt is made in this paper to explain on a scientific basis, for the benefit of the aviator, the phenomena he has observed, and at the same time to gather from these experiences such facts as are of value to the meteorologist in amplifying his knowledge of what actually exists in the upper air.

The disturbances of the air due to daytime convection are one of the prime sources of bumpiness. Especially on hot summer days do strong, rapidly rising currents of air penetrate to great altitudes and, where encountered, jolt the aeroplane. Where the cooler air is descending, the effect is similar to that of falling into a “hole.” The height to which the effects of surface roughness extend when the wind is blowing depends upon the speed of the surface wind and the height, of the obstruction.

In the free air, aviators' observations show how the layers of air flow over one another, the interface sometimes being marked by clouds and sometimes entirely invisible. At such levels are encountered billows or waves, and considerable difficulty is sometimes experienced in flying through such regions. Clouds, rain, and fog all contribute to the discomfort and danger of flying.

Perhaps the most interesting are the experiences in the thunder-storm and the up-and-down winds which accompany such storms. As the driving wedge of cold air at the surface advances ahead of the storm, the air into which the storm is moving is forced upward. The maximum turbulence is found in the region of the squall cloud, but the force of the rising air ahead of the storm is sufficient to carry up airplanes considerably, in spite of the efforts of the pilots to keep the nose of the plane down. The dangers from lightning and hail, are also quite as important as those from the capricious winds.