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206 Other inventors are working on rocket planes in various parts of the world. Some of these are be­ing developed solely to find a substitute for conven­tional power plants. Others have behind them enthusiasts who seek to travel to far places, with the moon as a favorite location.

Of course such projects have more than the problem of attaining speed to solve. Such craft, like the stratosphere plane which I have mentioned before, have to be very strong and sealed to protect human life. A supply of oxygen for the journey must be taken along far beyond the “seven mile limit” where the air is not dense enough for earth beings to breathe. Only once,—so far—has the stratosphere been penetrated. That was in the flight of August Piccard and Paul Kitsen, who last year reached a height of 51,775 ft. in a special metal sphere attached to a balloon.

Of as much interest as speed, seem to be air­planes of gigantic size. No sooner had the DO-X been built to carry 162 passengers than plans for a flying boat double its size were announced by an­other concern. What the physical limits of these Gargantuan monsters are I do not know. If there aren’t any, perhaps their measure of usefulness will decide their proportions. So far, large units have not proved profitable in air line operation, and the shadow of economics always hovers above any de­velopment.

Every week one can read of proposed tailless planes, wingless planes, motorless planes, and even