A Revolutionary Demonstration

In Madison Square Garden, at the Electrical Exhibition of 1898, Tesla staged a scientific tour de force, a demonstration completely beyond the generally accepted limits of technology. His invention, covered in patent No. 613,809 (1898), took the form of a radio-controlled boat, a heavy, low-lying, steel craft about four feet long. Inasmuch as radio hadn't been officially patented yet (Tesla's basic radio patent was filed in September 1897, but granted in March 1900), examiners from the US Patent Office were reluctant to recognize improbable claims made in the application "Method of and Apparatus for Controlling Mechanism of Moving Vessels or Vehicles." Confronted with a working model, however, examiners quickly issued approval. In fact, Tesla had been walking around New York City since 1895 picking up radio signals generated in various high-frequency experiments; he had received them as far as thirty miles away, at West Point. With the invention or improvement of several more control elements, he was able in short time to put them to use. The Boat

Tesla's tublike craft powered itself; there were several large batteries on board. Radio signals controlled switches, which energized the boat's propeller, rudder, and scaled-down running lightssimple enough in concept, but quite difficult to accomplish with existing devices. Even registering the arrival of a radio signal pulse taxed the rudimentary technology. Tesla invented a new kind of coherer (a radio-activated switch) for this purpose, essentially a canister with a little metal oxide powder in it. The powder orients itself in the presence of an electromagnetic field, like radio waves, and becomes conductive. If the canister is flipped over, after the pulse's passage, the powder is restored to a random, nonconductive state. Tesla contrived for a number of things to happen when the coherer conducted, most importantly for a disk bearing several differently organized sets of contacts to advance itself one step. Thus, if the contacts had previously connected the combination "right rudder/propeller forward full/light off," the next step might combine "rudder center/propeller stop/lights on." And with the aid of a few levers, gears, springs, and motors all would be accomplished, including a final step, flipping the coherer over so that it was ready to receive the next instruction. Applications

The world of 1898 had little understanding or use for Tesla's brilliant idea. Though he rather darkly imagined a military clamor for such things as radio-guided torpedoes, government interest did not materialize. (In one of history's curious footnotes, Tesla's good friend Mark Twain wrote immediately to say he was anxious to represent Tesla in the sale of this "destructive terror which you have been inventing" to England and Germany.) The navy did finance some trials in 1916, but the money went to one of Tesla's competitors. He remarked bitterly he could find no listeners until his patent had expired. Tesla's fears (and Twain's business hopes) were misplaced. The world's military establishments discovered many destructive terrors, but radio-controlled devices didn't number among them in any significant way until late in the twentieth century, with refinements in rocketry and guided bombs. Radio control remained a novelty, an exciting field for experimentalists and specialists, until the launching of the Space Age and the orbiting of myriad commercial and military satellites, all under remote control. Inside the Lab Index