"Recurring to what had been done more than half a century ago by Hertz, when he concentrated electric waves upon a focal point by means of a concave mirror," said Hall, "I saw that the key I wanted lay in an extension of these experiments. At last I found that I could transform the energy of an engine into undulations of the ether, which, when they had been concentrated upon a metallic object, like a chunk of gold, imparted to it an intense charge of an apparently electric nature. Upon thus charging a metallic body enclosed in a vacuum, I observed that the energy imparted to it possessed the remarkable power of disrupting its atoms and projecting them off in straight lines, very much as occurs with a kathode in a Crookes's tube. But--and this was of supreme importance--I found that the line of projection was directly towards the apparatus from which the impulse producing the charge had come. In other words, I could produce two poles between which a marvellous interaction occurred. My transformer, with its concentrating mirror, acted as one pole, from which energy was transferred to the other pole, and that other pole immediately flung off atoms of its own substance in the direction of the transformer. But these atoms were stopped by the glass wall of the vacuum tube; and when I tried the experiment with the metal removed from the vacuum, and surrounded with air, it failed utterly. "This at first completely discouraged me, until I suddenly remembered that the moon is in a vacuum, the great vacuum of interplanetary space, and that it possesses no perceptible atmosphere of its own. At this a great light broke around me, and I shouted 'Eureka!' Without hesitation I constructed a transformer of great power, furnished with a large parabolic mirror to transmit the waves in parallel lines, erected the machinery and buildings here, and when all was ready for the final experiment I telegraphed for you." Prepared by these explanations I was all on fire to see the thing tried. Hall was no less eager, and, calling in his two faithful assistants to make the final adjustments, he led the way into what he facetiously named "the lunar chamber." "If we fail," he remarked with a smile that had an element of worriment in it, "it will become the 'lunatic chamber'--but no danger of that. You observe this polished silver knob, supported by a metallic rod curved over at the top like a crane. That constitutes the pole from which I propose to transmit the energy to the moon, and upon which I expect the storm of atoms to be centred by reflection from the mirror at whose focus it is placed." "One moment," I said. "Am I to understand that you think that the moon is a solid mass of artemisium, and that no matter where your radiant force strikes it a 'kathodic pole' will be formed there from which atoms will be projected to the earth?"