Although the subjects treated in the earlier chapters are here spoken of as new inventions, all of them are not recent in the strictest sense of the word, for men had been working on the central idea of some of them for many years before they actually were developed to a stage where they could be patented and sent out into the world. H. E. M. CONTENTS CHAPTER PAGE I. THE AEROPLANE 3 How a Scientist Who Liked Boys and a Boy Who Liked Science Followed the Fascinating Story of the Invention of the Aeroplane. II. AEROPLANE DEVELOPMENT 49 How the Inventors Carried On the Art of Aviation Until It Became the Greatest of All Sports and Then a Great Industry. III. AEROPLANES TO-DAY 91 Our Boy Friend and the Scientist Look Over Modern Aeroplanes and Find Great Improvements Over Those of a Few Years Ago. A Model Aeroplane. IV. ARTIFICIAL LIGHTNING MADE AND HARNESSED TO MAN'S USE 129 Our Friends Investigate Nikola Tesla's Invention for the Wireless Transmission of Power, by Which He Hopes to Encircle the Earth With Limitless Electrical Power, Make Ocean and Air Travel Absolutely Safe, and Revolutionize Land Traffic. V. THE MOTION PICTURE MACHINE 164 Machines That Make Sixteen Tiny Pictures Per Second and Show Them at the Same Rate Magnified Several Thousand Times. Motion Pictures in School. Our Boy Friend Sees the Whole Process of Making a Motion Picture Play. VI. ADVENTURES WITH MOTION PICTURES 195 Perilous and Exciting Times in Obtaining Motion Pictures. How the Machine Came to Be Invented and the Newest Developments in Cinematography. VII. STEEL BOILED LIKE WATER AND CUT LIKE PAPER 224 Our Boy Friend Sees How Science Has Turned the Greatest Known Heats to the Everyday Use of Mankind. VIII. THE TESLA TURBINE 263 Dr. Nikola Tesla Tells of His New Steam Turbine Engine, a Model of Which, the Size of a Derby Hat, Develops More Than 110 Horse Power. IX. THE ROMANCE OF CONCRETE 288 The One Piece House of Thomas A. Edison and Other Uses of the Newest and Yet the Oldest Building Material of Civilized Peoples, Seen By the Boy and His Scientific Friend. X. THE LATEST AUTOMOBILE ENGINE 320 Our Boy Friend and the Scientist Look Over the Field of Gasoline Engines and See Some Big Improvements Over Those of a Few Years Ago.