Note 4 — Chapter XXI · THE HOME-COMING.

Those readers who may be inclined to think this speed extravagant or impossible are requested to remember that the most recent experiments in aerodynamics have proved that the higher the speed of an aerial machine the less is the power required to support and propel it, or, to quote the words of Professor Langley, of the Smithsonian Institute, “One horse-power will transport a larger weight at twenty miles an hour than at ten, a still larger at forty miles an hour than at twenty, and so on with increasing economy of power with each higher speed up to some remote limit not yet attained in experiment.” Granted therefore the practically illimitable energy of the motive power supposed to be at the command of the Aerians, there is no reason why a ship of the dimensions of the Avenger should not be propelled at the enormous speed mentioned in the text.