"Four Young Explorers" is the third volume of the third series of the "All-Over-the-World Library." A young millionaire and his friends explore and have adventures throughout Asia. It is written by Oliver Optic, a pseudonym of William T. Adams who was a teacher and served as a member of the Massachusetts House of Representatives. He consulted many volumes in writing this book; and he takes great pleasure in mentioning among them the very interesting and valuable work of W. T. Hornaday, an accomplished traveler and scientist.