Simultaneously the two floating castles launched against the towering dome of defense the heaviest beams they could generate and project. Under that awful thrust Valeron's mighty generators shrieked a mad crescendo and her imponderable shield radiated a fierce, eye-tearing violet, but it held. Not for nothing had the mightiest minds of Valeron wrought to convert their mechanisms and forces of peace into engines of war; not for nothing had her people labored with all their mental and physical might for almost two-score days and nights, smoothly and efficiently as one mind in one body. Not easily did even Valeron's Titanic defensive installation carry that frightful load, but they carried it. * * * * * Then, like mythical Jove hurling his bolt--like, that is, save that beside that Valeronian beam any possible bolt of lightning would have been as sweetly innocuous a caress as young love's first kiss--Radnor drove against the nearer structure a beam of concentrated fury; a beam behind which there were every volt and every ampere that his stupendous offensive generators could yield. The Chloran defenses in turn were loaded grievously, but in turn they also held; and for hours then there raged a furiously spectacular struggle. Beams, rods, planes, and needles of every known kind and of every usable frequency of vibratory energy were driven against impenetrable neutralizing screens. Monstrous cannon, hurling shells with a velocity and of an explosive violence far beyond anything known to us of Earth, radio-beam-dirigible torpedoes, robot-manned drill planes, and the many other lethal agencies of ultra-scientific war--all these were put to use by both sides in those first few frantic hours, but neither side was able to make any impression upon the other. Then, each realizing that the other's defenses had been designed to withstand his every force, the intensive combat settled down to a war of sheer attrition. Radnor and his scientists devoted themselves exclusively to the development of new and ever more powerful weapons of offense; the Chlorans ceased their fruitless attacks upon the central dome and concentrated all their offensive power into two semicircular arcs, which they directed vertically downward upon the outer ring of the Valeronian works in an incessant and methodical flood of energy. They could not pierce the defensive shields against Valeron's massed power, but they could and did bring into being a vast annular lake of furiously boiling lava, into which the outer ring of fortresses began slowly to crumble and to dissolve. This method of destruction, while slow, was certain; and grimly, pertinaciously, implacably, the Chlorans went about the business of reducing Valeron's only citadel.