But the havoc they wrought as demolition bombs was neither their only nor their greatest damage. The seventy-five million cubic feet of free oxygen, driven downward and prevented from escaping into the open atmosphere by Radnor's forces, quickly diffused into a killing concentration throughout the Chloran city save inside that one upstanding dome. Almost everywhere else throughout that city the natives died exactly as had died the people of the Valeronian village in the strangling chlorine of the invaders; for oxygen is as lethal to that amœbic race as is their noxious halogen to us.
Long before the bombs reached the ground Radnor was probing with his spy ray at the great central dome from within which Klynor Siblin's message had in part been sent. But now he could not get through it; either they had detected Siblin's beam and blocked that entire communication band or else they had already put up additional barriers around their headquarters against his attack, quickly though he had acted.
Snapping off the futile visiray, he concentrated his destructive beam into a cylinder of the smallest possible diameter and hurled it against the dome; but even that frightful pencil of annihilation, driven by Radnor's every resource of power, was utterly ineffective against that greenly scintillant hemisphere of force. The point of attack flared into radiant splendor, but showed no sign of overloading or of failure.
Knowing now that there was no hope at all of rescuing Siblin and that he himself had only a few minutes left in which to work, Radnor left his beam upon the dome only long enough for his recording photometers to analyze the radiations emanating from the point of contact. Then, full-driven still, but now operating at maximum aperture, he drove it in a dizzying spiral outwardly from the dome, fusing the entire unprotected area of the metropolis into a glassily fluid slag of seething, smoking desolation.
But beneath that dome of force there was a mighty fortress indeed. It is true that her offensive weapons had not seen active service for many years; not since the last rebellion of the slaves had been crushed. It is also true that the Chloran officers whose duty it was to operate these weapons had been caught napping—as thoroughly surprised at that fierce counterattack as would be a group of Earthly hunters were the lowly rabbits to turn upon them with repeating rifles in their furry paws.
But it did not take long for those officers to tune in their offensive armament, and that armament was driven by no such puny engines as Radnor's space ship bore. Being stationary and a part of the regular equipment of a fortress, their size and mass were of course much greater than anything ordinarily installed in any vessel, of whatever class or tonnage. Also, in addition to being superior in size and number, the Chloran generators were considerably more efficient in the conversion and utilization of interatomic energy than were any then known to the science of Valeron.
Therefore, as Radnor had rather more than expected, he was not long allowed to wreak his will. From the dome there reached out slowly, almost caressingly, a huge arm of force incredible, at whose first blighting touch his first or outer screen simply vanished—flared through the visible spectrum and went down, all in the veriest twinkling of an eye. That first screen, although the weakest by far of the four, had never even radiated under the heaviest test loads that Radnor had been able to put upon it. Now he sat at his instruments, tense but intensely analytical, watching with bated breath as that Titanic beam crashed through his second screen and tore madly at his third.
Well it was for Valeron that day that Radnor had armed and powered his vessel to withstand not only whatever forces he expected her to meet, but had, with the true scientific spirit and in so far as he was able, provided against any conceivable emergency. Thus, the first screen was, as has been said, sufficiently powerful to cope with anything the vessel was apt to encounter. Nevertheless, the power of the other defensive courses increased in geometrical progression; and, as a final precaution, the fourth screen, in the almost unthinkable contingency of its being overloaded, threw on automatically in the moment of its failure an ultimately impenetrable zone of force.
That scientific caution was now to save not only Radnor's life, but also the whole civilization of Valeron. For even that mighty fourth screen, employing in its generation as it did the unimaginable sum total of the power possible of production by the massed converters of the space flyer, failed to stop that awful thrust. It halted it for a few minutes, in a blazingly, flamingly pyrotechnic display of incandescence indescribable, but as the Chlorans meshed in additional units of their stupendous power plant it began to radiate higher and higher into the ultra-violet and was certainly doomed.