At the end of the 19th century, radio or wireless technology was in an early stage of development and the Marconi Company was engaged in development and construction of radio communication systems. Guglielmo Marconi appointed English physicist John Ambrose Fleming as scientific advisor in 1899. Fleming had been engaged as scientific advisor to Edison Telephone (1879), as scientific advisor at Edison Electric Light (1882), and was also technical consultant to Edison-Swan.[17] One of Marconi's needs was for improvement of the detector, a device that extracts information from a modulated radio frequency. Marconi had developed a magnetic detector, which was less responsive to natural sources of radio frequency interference than the coherer, but the magnetic detector only provided an audio frequency signal to a telephone receiver. A reliable detector that could drive a printing instrument was needed. As a result of experiments conducted on Edison effect bulbs,[14] Fleming developed a vacuum tube that he termed the oscillation valve because it passed current in only one direction.[18] The cathode was a carbon lamp filament, heated by passing current through it, that produced thermionic emission of electrons. Electrons that had been emitted from the cathode were attracted to the plate (anode) when the plate was at a positive voltage with respect to the cathode. Electrons could not pass in the reverse direction because the plate was not heated and not capable of thermionic emission of electrons. Fleming filed a patent for these tubes, assigned to the Marconi company, in the UK in November 1904 and this patent was issued in September 1905.[19] Later known as the Fleming valve, the oscillation valve was developed for the purpose of rectifying radio frequency current as the detector component of radio receiver circuits.[14][20]