How did people make phone calls before?

The research on long-distance sound transmission in Europe began in18th century. In 1796, Hughes proposed the method of transmitting voice information through microphone relay. Although this method is not practical, he gave this way of communication a name-telephone, which has been used ever since. 186 1 year, a german teacher invented the most primitive telephone, which can make short-distance calls by using the principle of sound waves, but it can't really be put into use. How to connect current and sound waves to realize long-distance call? Alexander bell is destined to accomplish this historic task. He systematically studied human voice, sound production mechanism and sound wave vibration principle. In the process of designing hearing AIDS for the deaf, he found that the spiral coil made noise at the moment when the current was cut off. This discovery suddenly occurred to Jambers-"Use the strength of current to simulate the change of sound size, so as to transmit sound with current." From then on, Bell and his assistant Watson began the arduous process of designing telephones. 1On June 2, 875, Bell and Watson were working on the final design and improvement of the model. It's time for the final exam. Watson put his ear to the speaker in another room with closed doors and windows, ready to answer. Bell accidentally spilled sulfuric acid on his leg during the last operation. He cried out in pain, "Mr. Watson, come and help me!" " Unexpectedly, this sentence reached the ears of Mr. Watson, who works in another room, through the telephone in his experiment. This very common sentence, however, became the first voice transmitted by telephone and went down in history. 1June 2, 875 was also commemorated as a great day for the invention of the telephone, and this place, Court Road 109 in Boston, USA, also went down in history. Up to now, a bronze medal has been nailed to its door, which reads: "The telephone was born here on June 2nd, 1875." 1On March 7th, 876, Bell was granted a patent for telephone invention with the patent number: 174655. 1877, the year after Bell invented the telephone, the first telephone lines were opened in Boston and new york, which are 300 kilometers apart. It was also in this year that someone sent news information to the Boston Globe by telephone for the first time, and the era of using public telephones began. Within a year, Bell installed 230 telephones and established Bell Telephone Company, the predecessor of AT&T.. Telephone was introduced to China on 188 1. British electrical technician Pi Xiaopu set up a pair of outdoor telephones along the street in Shanghai Shiliupu, and paid 36 francs for each call. This is the first telephone in China. 1882 In February, Danish Dabei Telegraph Company set up the first telephone office in China on Yangyutian Road, Shanghai Bund, with 25 users. 1889, Peng mingbao, an alternate in Anqing, Anhui province, designed a telephone by himself, including 50 or 60 kinds of homemade parts, which became the first telephone designed and manufactured by himself in China. At first, there was no dialing. All calls are made through the operator, who connects the caller to the right line. Dialing began in the early 20th century, when measles was prevalent in Massachusetts, and a physician worried that once the operator got sick, the whole city would be paralyzed. However, in China in 1970s, some districts and counties still used hand-operated telephones powered by dry batteries, and there was no dial. Today, there are about 750 million telephone users in the world.