Edison had been in the electrical business since the late 1870s, and within a decade was operating in the neighborhood of 1500 generating stations, including isolated plants associated with individual factories or other commercial installations, as well as central stations, supplying electricity to the public at large. The DC systems were basically lighting systems, too, but there was a DC motor for street-rail traction, and DC motors were beginning to be used for various manufacturing purposes.
The motors were made by the Sprague Electric Railway and Motor Company. Frank J. Sprague, a U.S. Naval Academy graduate, invented the DC motor. After naval service, he worked for the Edison Company for a while, but because Edison wasn't much interested in motors (or industrial applications of electricity in general) Sprague quit to form his own company in 1884. In the early years, when an Edison installation required a motor, the Sprague company supplied it
In 1882, Tesla began working for the Continental Edison Company in France, designing and making improvements to electrical equipment. He worked for about a year for the French branch of the Edison Electric Light Co. At the beginning of 1884, after successfully performed tasks in Strasbourg, Tesla returned to the headquarters of the Edison Continental Company in Paris. He hoped in vain that the professionals would take interest in his inventions of the rotating magnetic field and asynchronous motor. Bachelor, the U.S. manager of the French branch of the Edison Company advised him to seek his fortune in the New World.
In June 1884, Nikola Tesla arrived in the United States. On the way to the boat he actually lost all his possessions (train ticket and personal assets) and he arrived with just 4 cents in his pocket. Anyway the USA was considered the land of the free.
Thanks to the exceptional recommendation by Bachelor and successfully performed test given by Edison (repair of dynamo machines at the Oregon ship) Tesla was employed with Edison Machine Works. To this twenty-eight-year old enthusiastic expert Edison gave a very delicate job of redesigning and improvement of dynamo-machines produced in his factories for the ever-increasing market. The direct current electrification era had begun in the first place with great towns such as New York.
Tesla had expected that Edison, being such a great inventor, would perfectly understand and accept the concept of development of alternate currents devices and systems as a more convenient solution for production, transmission, distribution and use of electric energy. However, he was not understood again, and for that reason he left Edison's company disappointed after less than one year.
Tesla assumed that his arc lighting system would be valuable to the Edison organization and that he would handsomely rewarded for his work. However, when that didn’t happen, Tesla quit in disgust and found new backers in Rahway, New Jersey who helped him to patent and build his own arc-lighting system. However, once the Rahway businessmen had a lighting system up and running, they fired Tesla. Destitute, Tesla returned to New York to dig ditches.
Fortunately, Tesla helped dig ditches for the installation of cables connecting the headquarters of the Western Union Telegraph Company with stock and commodity exchanges and he came to the attention of Alfred S. Brown who was supervising the work. Brown took a liking to Tesla and introduced him to Charles Peck, a lawyer who had just made a fortune by forcing Jay Gould to buy his Mutual Union Telegraph Company.
In March 1885 Tesla applied his first patent on the improvement of arc lamp regulator. At the same time he registered his 'Tesla Arc Light Co'.
Edison and Tesla corresponded in the 1890s over X-rays and may have worked together; we don't have Tesla's letters to Edison, but Edison wrote to Tesla on 18 March 1896:
"My dear Tesla, Many thanks for your letter. I hope you are progressing and will give us something that will beat Roentgen."
In response to a critical essay to be published in the Electrical Review in May of 1896, Edison said he didn't care what the article stated for his own sake, but he added:
"Tesla is of a nervous temperament and it will greatly grieve him and interfere with his work. While Tesla gives vent to his sanguine expectations when he should not do so, it must not be forgotten by [the article author] Mr Moore that Tesla is an experimenter of the highest type and may produce in time all that he says he can."
The X-ray experiments were too dangerous and the radiation emitted caused cancer and nearly blinded Edison and ultimately killed his assistan Clarence Dally. He personally supported Dally's widow and children financially, and he never pursued X-ray research again. The event haunted him for the rest of his life, causing him to later remark:
“Don't talk to me about X-rays. I am afraid of them. I stopped experimenting with them two years ago, when I came near to losing my eyesight and Dally, my assistant practically lost the use of both of his arms. I am afraid of radium and polonium too, and I don't want to monkey with them."
That's hardly the language or activity of mortal enemies. However, it seems that the situation changed some years later when Edison became the partnership of Marconi and he criticized Tesla's idea of sending messages through the whole surface of the planet.
Tesla's Reply to Edison - English mechanic and world of science - July 14, 1905
A Bit of Sarcasm.
Permit me to say on this occasion that if there exist to-day no facilities for wireless telegraphic and telephone communication between the most distant countries, it is merely because a series of misfortunes and obstacles have delayed the consummation of my labors, which might have been completed three years ago. In this connection I shall well remember the efforts of some, unwise enough to believe that they can gain an advantage by throwing sand in the eyes of the people and retarding the progress of invention. Should the first messages across the seas prove calamitous to them, it will be a punishment regrettable but fully deserved.