It may interest readers of _The Young Wireless Operator_ series to know that most of the happenings in these books are based upon actual occurrences. Years ago, as a reporter, the author wrote for the New York _Sun_ the stories of the auction of bled wool, the cotton-lined cabin, the mystery of the wheat sacks, and other accounts of the work of the United States Secret Service, that appear in this present volume. Although some of the characters in the book are of course fictitious, others, like Sheridan of the Secret Service, are real characters who actually did the things they are portrayed as doing. Of course names have been changed. The practice of keeping note-books and clippings that had to do with work the writer was engaged in, has made all this material available for present use, and brought it once more freshly to mind. The descriptions of parts of New York and her wonderful waterways are written from intimate, personal knowledge of the places described. In effect, therefore, _The Young Wireless Operator—With the U. S. Secret Service_ is a true story. To make all the tales in this series true has been the earnest desire of the writer. That does not mean that every incident described necessarily happened. It does mean that the incidents used are not only possible under the circumstances, but probable, and that the descriptions are exact and accurate. The picture of life portrayed is in each case as exact as careful observation and careful writing can make it. Before the author prepared the preceding volume of this series, _The Young Wireless Operator—With the Oyster Fleet_, he first went to the Delaware Bay and made a cruise on an oyster boat, living aboard with the crew and sharing their life and labors. Furthermore, he had lived for twenty years in that country and had spent many weeks, in all, cruising about on oyster boats. The writing of _The Young Wireless Operator—Afloat_, which deals with both New York City and ports on the Mexican Gulf was made possible by residence for some months on the Gulf, and through the coöperation of Southern newspaper men. Practically all the incidents related concerning the tidal wave that destroyed Corpus Christi are stories of actual occurrences, gathered by newspaper men on the spot. Most of the ships described in that story are real vessels and were actually afloat at the time and in the positions given to them by the author. The wireless stations and wireless calls are also real.