Almos’ knowledge of such matters made me instantly aware of all this the moment the question of buoyancy presented itself in my mind, but, although I could not help marveling at the ingenuity of this wonderful people, I outwardly preserved the calm demeanor which Almos’ strong personality had made a characteristic.  Indeed, Reon, who had been preparing an aerenoid for our use—­such was the Martian name for these airships—­was quite unaware of my astonishment, and it was plain that with the exercise of due care, when I spoke without the prompting of Almos’ knowledge, there was no likelihood of anyone’s having a suspicion of my true personality.

The aerenoid in which we were going to make our journey differed in appearance considerably from those which I saw floating about us.  Cigar-shaped, with windows in its sides and roof like a steamer’s portholes, it more nearly resembled a submarine boat than an airship, as it rested on a platform built in the side of the balcony for the purpose.  Yet such was the repelling force of this wonderful metal which the Martians had discovered, and which I found was attached in two or more strips to the bottom of the aerenoids, that the matter of weight in their construction was of little importance.  While resting on the ground these strips were encased in a material that was a non-conductor, thus neutralizing the repelling force.  In order to raise the car the casing was merely drawn back by means of a controlling lever, until enough of the metal was exposed to the surface of Mars to cause the repelling force to lift the aerenoid, and by preserving this exposure, any desired height could thus be attained.

The entire design of this aerenoid indicated that it was built to attain great speed, and yet as I stepped into it through a door that closed flush with the rounded sides, I was astonished at seeing no traces of machinery.  Instantly I became aware of the extraordinary means of propulsion, however, and so simple, yet so effective, was it, that I could not restrain a cry of admiration at this new evidence of scientific progress.

Atmospheric pressure, instead of retarding speed, was employed to produce it.  Under the floor of the car and occupying the entire rear half, was a chamber of steel, five or six feet broad at one end, and tapering down with the sides of the aerenoid until it reached the stern, where it ended in an opening one inch in diameter.  By a chemical process the air in the chamber was exhausted, instantly causing a vacuum.  Immediately the air outside the car rushed in through the small opening at the rear end, with such great force as to cause a concussion against the forward and broad end of the chamber, thus driving the aerenoid ahead.  So quick was this action that, when going at great speed, more than one hundred exhaustions would occur in a minute.  Simple though this means of propulsion was, gravity having been overcome and the long pointed body of the aerenoid offering little resistance, the speed thus attained was remarkable.