Following Nikola Tesla On His Work With Alternating Currents, this book is the second in a three part Tesla Presents series offering the reader what has been, up until now, unavailable material on the pioneering work of Nikola Tesla in field of radio frequency electrical engineering. While first delivered under the title "On the Streams of Lenard and Roentgen with Novel Apparatus for Their Use" the information carried within the text of the lecture goes far beyond this topic. In addition to his opening remarks on X-ray discovery, a major portion of Tesla's commentary deals with the specially designed high frequency resonators that were used in conjunction with his work, plus clear descriptions of stroboscopic instruments he designed for measurement of frequency and phase. Other topics addressed include wireless receiving methods and the genesis of Tesla's particle beam projector of 1937. During the talk Tesla had displayed approximately 120 drawings of specially constructed vacuum tubes, many being of the Lenard type and also the single-electrode type of his own design. Also among the drawings were renderings of various tubes used in his wireless communications experiments. Enhanced photographs of these images are among the 30 illustrations which fill out this fine volume.