Arduous work was at once resumed at home on duplex and quadruplex telegraphy, just as though there had been no intermission or discouragement over dots twenty-seven feet long. A clue to his activity is furnished in the fact that in 1872 he had applied for thirty-eight patents in the class of telegraphy, and twenty-five in 1873; several of these being for duplex methods, on which he had experimented. The earlier apparatus had been built several years prior to this, as shown by a curious little item of news that appeared in the Telegrapher of January 30, 1869: "T. A. Edison has resigned his situation in the Western Union office, Boston, and will devote his time to bringing out his inventions." Oh, the supreme, splendid confidence of youth! Six months later, as we have seen, he had already made his mark, and the same journal, in October, 1869, could say: "Mr. Edison is a young man of the highest order of mechanical talent, combined with good scientific electrical knowledge and experience. He has already invented and patented a number of valuable and useful inventions, among which may be mentioned the best instrument for double transmission yet brought out." Not bad for a novice of twenty-two. It is natural, therefore, after his intervening work on indicators, stock tickers, automatic telegraphs, and typewriters, to find him harking back to duplex telegraphy, if, indeed, he can be said to have dropped it in the interval. It has always been one of the characteristic features of Edison's method of inventing that work in several lines has gone forward at the same time. No one line of investigation has ever been enough to occupy his thoughts fully; or to express it otherwise, he has found rest in turning from one field of work to another, having absolutely no recreations or hobbies, and not needing them. It may also be said that, once entering it, Mr. Edison has never abandoned any field of work. He may change the line of attack; he may drop the subject for a time; but sooner or later the note-books or the Patent Office will bear testimony to the reminiscent outcropping of latent thought on the matter. His attention has shifted chronologically, and by process of evolution, from one problem to another, and some results are found to be final; but the interest of the man in the thing never dies out. No one sees more vividly than he the fact that in the interplay of the arts one industry shapes and helps another, and that no invention lives to itself alone.