Nikola Tesla made his first discoveries and inventions on the eighties of the last century. Searching for a noncommutator motor which would have eliminated major defects of Graham's direct current motor, in 1882 Tesla brilliantly invented the multiphase alternating current induction motor. At the same time this motor was the solution which made long-distance energy transmission possible, due to the possibility of transforming alternating currents into high voltage for more efficient transmission and low voltage for practical use.
In the following two years Tesla made futile efforts to arouse interest in European experts and ensure funds for realization of the new system of electric power generation, transmission and utilization. Finally, in 1884, he went to the USA with the recommendation from his employer in Edison's Paris branch. Edison, who was already famous and rich owing to his numerous patents and a series of inventions, immediately offered a job to Tesla, but was not intersted in his alternating current, system. So their brief encounter ended and Tesla went his own way without Edison's encouragement and understanding.
Broke again, Tesla indulged in some investigations which rendered financial results and made it possible for him to continue struggle for application of the alternating current system. Bearing this in mind, we realize why Tesla's first patents applied for in 1885, 1886 and the first half of 1887 were in the field of electric-arc lamp regulators and-direct current generators. After these ten patents, the most important Tesla's patents in the field of polyphase alternating current followed. Since October 1887 patents were reeled off one after another: in 1887 Tesla applied for 7 patents, in 1888 for 11 and in 1889 even for 15. After this prolif ic phase the number of patents in the field of polyphase currents decreased to 6 in 1890 and only to 3 in 1891. In this year the change in the scope of Tesla's interests was noted, as Tesla gradually penetrated into the field of alter- nating currents of higher frequencies than those applicable in industry (frequencies of several dozen Hz, but not over 133 Hz). This change was ever more pronounced in the years to come. In 1891 Tesla submitted the application for his famous spark-gap oscillator with resonance transformer. In various forms these oscillators, in fact the only high frequency current gener ators those days, appeared in Tesla's patents between 1891 and 1896. Since 1897 a series of patents followed in the field of radiotechnology as well as electric circuit controllers. Among the patents from 1897 there were the two famous patents protecting his basic plan for the system with four adjusted circuits. Among the patents from 1898 the one protecting the apparatus for and method of controlling mechanism of moving objeets stood out. In 1899 Tesla applied for four patents in tlzP field of radio and energy transmission through space. In the following 1900 six patents were applied for, mostly in the field of radio, while in 1901 Tesla had two patents Thich referred to radiant energy utilization. In 1902 Tesla applied for his list patent in the field of radio, which was issued to him only in 1914.
After a seven-year break Tesla recommenceci applying for patents, but this time in the field of turbines, pumps, Eluids, lightning protectors, flow-meters and speed indicators. The majority of these patents were applied for in 1916. 'The last two patents Tesla applied for in the USA in 1921 nd 1927 were in the domain of avionics.
The total number of patents issued to Nikola Tesla in the USA according to the evidence of the Nikola Tesla Museum in Belgrade amounted to 112. In the list of patents issued in the USA the patent no. 613.819 (Filings tube no.86) also exists, but there is no evidence that it was issued. The number of the patent was given in >>Wireless Telegraphy<<, the book written by Charles Henry Sewall (D. Van Nos i:rand Company, New York, 1904), but no other data but the title and the above number were supplied. Whether this patent was only applied for, and how many patents Tesla applied for but was never issued is beyond our ken. In the archives of the Nikola Tesla Museum in Belgrade there are materials which lead us to the conclusion that Tesla prepared even drawings for some patents, but such patents were not registered anywhere. It is interesting to note that many of these illustrations represented apparatuses to be used in radiotechnology.
The list of patents issued to Tesla in other countries was compiled on the basis of documents in the archives of the Nikola Tesla Museum in Belgrade. It is published for the first time and we cannot grant that it is complete. The total number of countries encompassed by the list is 25, and the total number of patents is 109. It is interesting to note that no patents in the field of power engineering are included and that the first patents refer to Tesla's spark-gap oscillator from 1891. Tesla patented his remotely controlled vehicle in ten countries. The majority of patents were applied for between 1896 and 1901 (radio, conductor insullation, remotely controlled vehicle); another Tesla's prolific period was in 1910 (fluid turbines, pumps).
Tesla obtained the majority of his foreign patents in Great Britain (the total of 16), including his last patents in 1922. Among these were two patents which had not been issued to hirz3 in the USA. One of them referred to balancing rotating machine parts, while the other concerned the improved process of production of high vacuum.
Although most patents issued to Tesla outside the USA were repetitions of what he had obtained in the USA, for those who study Tesla's work these patents can offer additional explanations and more precise formulations of his ideas, discoveries and inventions.

Prof. dr Aleksandar Marinčić