The Boys' Book of Model Aeroplanes

The aviator must venture in his frail craft upon an unknown and uncharted sea. The great problem is to ride the shifting air currents and keep the machine right side up. Although we cannot see the air currents, we know that they are constantly ebbing and flowing, piling themselves in great heaps, or slipping away in giddy vortices. There is much beautiful scenery, high mountain peaks, deep valleys, and level plains formed by these ever shifting air currents through which the aviator must steer his course blindly as best he may. A great bank of whirling clouds driven before the wind shows how rough and tumbling a sea he must navigate.