Heinrich Hertz published the first review of the phenomenon in 1889. By 1911, Major General George Owen Squier was conducting some of the earliest studies designed to put carrier current transmissions, which he called "wired wireless", to practical use. To be effective, the radio transmitter must be capable of generating pure continuous-wave AM transmissions. Thus, the technology needed to set up carrier current transmissions would not be readily available until the late 1910s, with the development of vacuum tube transmitters and amplifiers. Long-distance communication The first commercial applications of carrier current technology included the setting up of long-distance telegraph, telemetry, and telephone communication by electrical companies over their high-voltage distribution lines. This approach had a major advantage over standard telegraph and telephone lines, because radio signals can readily jump over any small gaps in cases when there is a line break. In May 1918, the Imperial Japanese Electro-Technical Laboratory of Tokyo successfully tested "wave telephony" over the Kinogawa Hydro-Electric Company's 144-kilometer (90-mile) long power line. In the summer of 1920, a successful test transmission over 19.2 kilometers (12 miles) of high-tension wires was reported from New Jersey, and by 1929, 1,000 installations had been made in the United States and Europe. The majority of power line communication installations use transmissions in the longwave band, to avoid interference to and from standard AM stations. Home entertainment services United States In 1923, the Wired Radio Service Company, a subsidiary of the local electric company, set up a subscription news and entertainment service at Staten Island, New York that used carrier current transmissions over the electrical power lines. To receive the transmissions, subscribers had to lease a receiver costing between two and five dollars a month. However, despite the power company's optimism that the system would eventually be installed nationally, the effort proved unable to compete with the free offerings provided by standard radio stations. General Squier continued to unsuccessfully promote the technology for home entertainment, until 1934, when he helped found the Muzak company, which focused on the business market. Europe Carrier current home entertainment services would prove to be more popular in Europe. Previously, there had been a few successful telephone newspaper services, which sent entertainment to subscribers over standard telephone lines. However, carrier current transmissions had the ability to provide programs over telephone lines without affecting the regular telephone service, and could also send multiple programs simultaneously. In Germany, the