Nelson saw one of the armored cannoneers bend forward, firmly grasp a short lever with both hands. In anticipation of a terrific report, the aviator pressed finger tips to his ears. There followed not a thundering crash, but a curious, eery, high-pitched scream, rather like that of a fire siren. There was no smoke! Nelson's incredulous eyes sought the muzzle of the gun and detected issuing from it what appeared to be a thin, white rod. This shimmering stream of silver shot straight towards the pine tree, gradually widening and giving off feathery billows of steam. In a fraction of a moment the target was completely veiled from sight in a furious pall of clouds which, to Nelson's great astonishment, did not dissipate nor condense with the speed of ordinary steam. "Nava!" With impressive suddenness the screaming sound faded, leaving a sort of stunned silence on the gun platform. The gunners stalked back to their original stations. * * * * * Slowly, reluctantly, the mist enveloping the pine tree cleared away and Nelson felt a chill creeping up his spine. The pine was a good three hundred yards away, yet now it sagged limp to earth, stripped of bark, twigs and needles, only the bright yellow trunk and major branches remaining. "That tree was a good two feet thick," mused the astounded aviator, "yet the steam gun bent it like a sapling. My God! What would it do to a man?" "What thinkest thou of our retortii?" The Atlantean's beard glinted like metal as he shook with a grim, silent laughter. "These great retortii can shoot half a league and will blast any living thing in their path. I tell thee, friend Nelson, the discharge of even a small retortii will strip the flesh from a man's bones as a peasant strips the husk from an ear of corn!" "Fearful, terrible!" was Nelson's awed comment. "Is there no defence against them?" "Of course." The Hero's green feather-crested helmet gleamed with a nod. "Was there ever an instrument of war that had not its defence? Yea, we have the blue vapor to shatter steam particles--it is called the blue maxima. Thou wilt presently see some of our troops armed with it." "But where does this steam come from? How is it generated?" These two were the first of a host of questions which trembled on Nelson's lips. "The steam," replied the Atlantean, "comes from the earth. We compress it many times, then feed it into our retortii. Without the heat of Mother Earth and our flame suns we would all perish. Steam is our motive power, our defence and our enemy!" He flung his hand towards the vast valley stretched before them. It was hemmed in on either side by colossal breath-taking mountain ranges, whose caps shone and glittered with an eternal snow.