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To advance his experiments with high frequency, Tesla built a reciprocating engine, operable by air or steam, which led to an altercation with the Police Department. From watching the machine's vibrations, he was side-tracked into investigating the mechanical vibrations it caused. He came to believe that mechanical vibrational resonance was similar to the resonances of electric current. The "high-vibrations" machine he built worked too well. It operated strongly enough to raise neighborhood fears of an earthquake and caused the police shutdown of his experiments.
In September, 1898, Tesla was again front page news with his demonstration of a remotely-controlled robotic boat. The model boat was wirelessly controlled by the signals from Tesla's transmitter to its antenna and receiver and then to a servo-mechanism which translated the signal to a variety of maneuvers: starting, stopping, turning, etc. This was a remarkable combination of wireless telegraphy and robotics.
Tesla, an American citizen since 1889, offered this invention to the U.S. government but it was ridiculed and rejected. A patent was granted in November, 1898, but only after the Chief Examiner had visited New York to confirm the machine was really operable.
Next, Tesla returned to his experiments with power sources but having built an oscillator that produced four million volts, he had reached his laboratory's safety limitations and was short of money yet again.
An offer of much space and operating funds sent Tesla to Colorado Springs in May, 1899. The Tesla coil transformers in Colorado were huge, seventy-five feet in diameter and produced correspondingly large voltages and frequenciesartificial lightning bolts 135 ft long and accompanying thunder heard fifteen miles away. Tesla had charged the earth to a level that would only have been achievable by hundreds of natural lightning bolts. Enough power was used to overload and cause short circuits at the powerhouse of the Colorado Springs Electric Company. Again Tesla's experiments were curtailed and he returned to New York to report on his findings. Further details of the Colorado experiments remained locked in Tesla's imagination until he died.