“I am about to die. My physician tells me that I have less than a month left to work. I have just completed the apparatus which had engaged my attention exclusively for the last six years,--my wave-measuring machine. By means of this machine, any wave of a given intensity may be registered as regards its velocity and power.” “If you don’t mind, I’d like to break in right there,” I interrupted. “Go on,” said Tom. “What kind of waves is he talking about? Is this some sort of a machine for measuring the tides down on the beach, or what is it?” Tom laughed. “Not exactly,” he said. “Denckel’s machine is to measure waves like those of electrical energy. You know, don’t you, that we believe wireless messages go from one station to another by means of ether waves, as they call them?” I nodded. “Well, Denckel means to measure waves of that kind, and waves that would come from an arc lamp or a dynamo or a piece of radium or anything like that. It’s to measure the same sort of wave that charged the reflectoscopes, in short--See?” “I do,” I answered. “But--” “Hold on till we finish the letter, Jim, and we’ll go over it.” I subsided and Dorothy went on. “More than that, the distance from the point of generation of the wave, and the exact direction from which it comes, can be ascertained. It is, as you may see, the unique discovery of the past five years. In computing and making it, I have used some discoveries made by my late colleague, Professor Mingern. At his death, six years ago, he passed his work on to me. Now that my death approaches, I pass my work on to you. I have had many pupils in my long life, but none so worthy, none so able to carry on the work, as you, my dear friend and pupil. Farewell. “CARL DENCKEL.” “He was as fine an old chap as ever I knew,” said Tom, with deep feeling. “To think of his sending that to me. But what can have happened to it?” Dorothy stood with a second sheet in her hand. “Here’s something about it,” she said. “Manuscripts sent under cover to same address, apparatus sent to New York via Hamburg-American line.” “Then the first thing to do is to find the apparatus,” said Tom. “We can send a trailer after the manuscript, but we can’t bank on getting it. I’ll go down to the custom-house to-morrow morning. What a blow to science, if the whole thing were lost.” “But,” he went on suddenly, “isn’t it extraordinary that this should come along just now? It helps us a whole lot.” “That is so,” remarked Dorothy reflectively. “We ought to be able to tell just where ‘the man’ is every time.” “Once more I humbly confess my ignorance,” I remarked, “but will you kindly enlighten me as to the way in which this is to help us in the search for the man?”