her death, Tesla fell ill. He spent two to three weeks recuperating in Gospic and the village of Tomingaj near Gracac, his mother's birthplace.On 6 June 1884, Tesla first arrived in the United States, in New York City[25] with little besides a letter of recommendation from Charles Batchelor, a former employer. In the letter of recommendation to Thomas Edison, it is claimed that Batchelor wrote, 'I know two great men and you are one of them; the other is this young man', but the exact contents of the letter is disputed in McNichol's book. Edison hired Tesla to work for his Edison Machine Works. Tesla's work for Edison began with simple electrical engineering and quickly progressed to solving some of the company's most difficult problems. Tesla was even offered the task of completely redesigning the Edison company's direct current generators.[26]Tesla claimed he was offered US$50,000 (~ US$1.1 million in 2007, adjusted for inflation)[27] if he redesigned Edison's inefficient motor and generators, making an improvement in both service and economy.[28] In 1885 when Tesla inquired about the payment for his work, Edison replied, "Tesla, you don't understand our American humor," thus breaking his word.[29][30] Earning US$18 per week, Tesla would have had to work for 53 years to earn the amount he was promised. The offer was equal to the initial capital of the company. Tesla immediately resigned when he was refused a raise to US$25 per week.[31]Tesla, in need of work, eventually found himself digging ditches for a short period of time for the Edison company. He used this time to focus on his AC polyphase system.[32]Middle years Wireless transmission of power and energy demonstration during his high frequency and potential lecture of 1891Electromechanical devices and principles developed by Nikola Tesla: Various devices that use rotating magnetic fields (1882)The Induction motor, rotary transformers, and "high" frequency alternatorsThe Tesla coil,[33] his magnifying transmitter, and other means for increasing the intensity of electrical oscillations (including condenser discharge transformations and the Tesla oscillators[34][35])Alternating current long-distance electrical transmission system[36] (1888) and other methods and devices for power transmissionSystems for wireless communication (prior art for the invention of radio) and radio frequency oscillators[37]Robotics and the electronic logic gate[38]Electrotherapy Tesla currents[39][40][41]Wireless transfer of electricity and the Tesla effect[42][43]Tesla impedance phenonomena[44]Tesla electro-static fieldTesla principleBifilar coilTelegeodynamicsTesla insulationTesla impulses[45]Tesla frequencies[33]Tesla discharge[33]Forms of commutators and methods of regulating third brushesTesla turbines (e.g., bladeless turbines) for water, steam and gas and the Tesla pumpsTesla igniterCorona discharge ozone generatorTesla compressorX-rays Tubes using the Bremsstrahlung processDevices for ionized gases and "Hot Saint Elmo's Fire".[46]Devices for high field emissionDevices for charged particle beamsPhantom streaming devices[47]Arc light systemsMethods for providing extremely low level of resistance to the passage of electric current (predecessor to superconductivity)Voltage multiplication circuitryDevices for high voltage dischargesDevices for lightning protectionVTOL aircraftDynamic theory of gravityConcepts for electric vehiclesPolyphase systems In 1886, Tesla formed his own company, Tesla Electric Light & Manufacturing. The initial financial investors disagreed with Tesla on his plan for an alternating current motor and eventually relieved him of his duties at the company. Tesla worked in New York as a laborer from