He smiled, but made no reply. Still the strange process continued. The pink vapor became so dense that the lump of gold was no longer visible, although the eye of violet light glared piercingly through the colored fog. Every second the deposit of metal, shining like a mirror, increased, until suddenly there came a curious whistling sound. Hall, who had been adjusting the mirror, jerked away his hand and gave it a flip, as if hot water had spattered it, and then the light in the tube quickly died away, the vapor escaped, filling the room with a peculiar stimulating odor, and I perceived that the end of the glass tube had been melted through, and the molten gold was slowly dripping from it. "I carried it a little too far," said Hall, ruefully rubbing the back of his hand, "and when the glass gave way under the atomic bombardment a few atoms of gold visited my bones. But there is no harm done. You observed that the instant the air reached the kathode, as I for convenience call the electrified mass of gold, the action ceased." "But your anode, to continue your simile," I said, "is constantly exposed to the air." "True," he replied, "but in the first place, of course, this is not really an anode, just as the other is not actually a kathode. As science advances we are compelled, for a time, to use old terms in a new sense until a fresh nomenclature can be invented. But we are now dealing with a form of electric action more subtile in its effects than any at present described in the text-books and the transactions of learned societies. I have not yet even attempted to work out the theory of it. I am only concerned with its facts." "But wonderful as the exhibition you have given is, I do not see," I said, "how it concerns Dr. Syx and his artemisium." "Listen," replied Hall, settling back in his chair after disconnecting his apparatus. "You no doubt have been told how one night the Syx engine was heard working for a few minutes, the first and only night work it was ever known to have done, and how, hardly had it started up when a fire broke out in the mill, and the engine was instantly stopped. Now there is a very remarkable story connected with that, and it will show you how I got my first clew to the mystery, although it was rather a mere suspicion than a clew, for at first I could make nothing out of it. The alleged fire occurred about a fortnight after our discovery of the double tunnel. My mind was then full of suspicions concerning Syx, because I thought that a man who would fool people with one hand was not likely to deal fairly with the other.