As indicated on the title-page, "The Boy Travellers on the Congo" is condensed from that remarkable narrative, "Through the Dark Continent," by one of the most famous explorers that the century has produced. The origin of the present volume is sufficiently explained in the following letter: "EVERETT HOUSE, NEW YORK, _December_ 1, 1886. "MY DEAR COLONEL KNOX,--It is a gift to be able to write to interest boys, and no one who has read your several volumes in the 'Boy Traveller' series can doubt that you possess this gift to an eminent degree. While reading those interesting and valuable books of yours, I have regretted that they were not issued in the time of my own youth, so that I might have enjoyed as a boy the treat of their perusal. Now, the Harpers desire a condensation of my two volumes, 'Through the Dark Continent,' to be made for young folks, but I have neither the time, nor the experience in juvenile writing, for performing the work. I suggest that you shall produce a volume for your series of 'Boy Travellers,' and assure you that it would delight me greatly to have you take your boys, who have followed you through so many lands, on the journey that I made from Zanzibar to the mouth of the Congo. "There is too much in my work in its present form for their mental digestion; but, narrated in that chaste and forcible style which has proved so entertaining to them, they would certainly find the journey through Africa of exceeding interest when made in your company. By all means take Frank and Fred to the wilds of Africa; let them sail the equatorial lakes, travel through Uganda, Unyoro, and other countries ruled by dark-skinned monarchs, descend the magnificent and perilous Congo, see the strange tribes and people of that wonderful land, and repeat the adventures and discoveries that made my journey so eventful. You have my full permission, my dear friend, to use the material in any way you deem proper in adapting it to the requirements of the 'Boy Travellers.' "Sincerely yours, as always, HENRY M. STANLEY. "TO COLONEL THOS. W. KNOX." The preparation of this book has been a double pleasure--first, to comply with the wishes of an old friend, and secondly, to carry the boys and girls of the present day to the wonderful region that, until very recently, was practically unknown. I have the fullest confidence that they will greatly enjoy the journey across equatorial Africa from the eastern to the western sea, and eagerly peruse every line of Mr. Stanley's narrative of discovery and adventure.