It does not describe any old or obsolete forms of wireless apparatus but only the latest types of aerials, spark coils, keys, gaps, condensers, helixes, oscillation transformers, loose couplers, tuning coils, detectors, loading coils, variable condensers, aerial switches, etc. IT IS ONE OF THE MOST DETAILED AND THOROUGH BOOKS EVER PUBLISHED. The information is all intensely practical. Complete directions and dimensions are given. Nothing is left to be guessed at. The book must really be seen to be appreciated. *Partial Contents* Chapter I.—THE AERIAL. The Location of the Station. The Construction of an Operating Bench. The Aerial and Ground. The Supports or Masts. Types of Aerials. How to Erect an Aerial. Protection from Lightning, Etc. Chapter II.—SPARK COILS. The Construction of Spark Coils. A 1/4-inch Spark Coil. A 1/2-inch Spark Coil. A 1-inch Spark Coil. A 1 1/2-inch Coil. A 2-inch Coil. Sources of Current. Dry Cells. Storage Cells. Wireless Keys, Etc. Chapter III.—TRANSMITTING APPARATUS AND ITS CONSTRUCTION. Step-down Transformers. Spark Gaps. The Oscillation Condenser. Leyden Jars. Helixes. Oscillation Transformers, Etc. Chapter IV.—THE RECEIVING APPARATUS AND ITS CONSTRUCTION. A Silicon Detector. A Galena Detector. The Double Slide Tuning Coil. How to Make a Fixed Condenser. Building a Loose Coupler. The Loading Coil. How to Make a Variable Condenser, Etc. Chapter V.—ARRANGEMENT AND OPERATION OF THE APPARATUS. Aerial Switches. The Buzzer Test. Using More Than One Detector. Shunting the Detector. Complete Outfits. Portable Sets. The Operation of the Station, Etc. *LESSONS IN WIRELESS TELEGRAPHY* FOURTH EDITION 72 Pages 66 Illustrations A systematic course in the elementary principles. Written so you can understand it. In 35 lessons. 1.—Magnetism. 2.—Magnetic Induction. 3.—Primary and Secondary Cells. 4.—Electric Currents. 5.—Electromagnetism. 6.—Dynamo-Electric Machinery. 7.—The Induction Coil. 8.—The Transformer. 9.—Leyden Jars and Condensers. 10.—Electromagnetic Theory. 11.—Electric Waves. 12.—Principles of Wave Telegraphy. 13.—The Aerial. 14.—The Wireless Coil. 15.—The High Potential Transformer. 16.—The Oscillation Condenser. 17.—The Helix. 18.—Spark Gaps. 19.—The Key. 20.—Aerial Switches. 21.—Anchor Gaps. 22.—Detectors. 23.—Tuning Coils. 24.—Loose Couplers. 25.—Fixed Condensers. 26.—Variable Condensers. 27.—Telephone Receivers. 28.—Hot Wire Ammeter. 29.—Potentiometer. 30.—Dead End Losses and Switches. 31.—Distributed Capacity. 32.—Poulsen Arc. 33.—Receiving Undamped Waves. 34.—The Audion Amplifier. 35.—Hook-Ups. *Price, 25 Cents, Postpaid* If you want to understand your apparatus and how it works, you will need this book—over 15,000 copies in use. *Price, 25 Cents, Postpaid* *Model Flying Machines*