The soap bubble and the projectile illustrate the two opposite extremes of mechanical flight.

The two greatest hindrances to the solution of this problem have always been the balloon and the screw propeller.

People pick up this and that old device, and fancy that a merely new combination will answer their purpose. The balloon is one such device, having one chief function— that of flotation. Balloon troubles and risks are so well-known to every member of this Society that they need no description. The very obvious schoolboy device of elongating the bulb and driving it end-on with a screw propeller has only resulted in the attainment of a feeble speed, not hitherto exceeding 10 miles an hour in a dead calm.