Seeing the telegram in the early movies, the operator kept pressing it with his finger and sent it out? What is the principle?

The principle of telegraph is that in the carrier control of transmitting equipment, the length and quantity of carrier output and the output interval are controlled by "switch" (the key of telegraph); In this way, a set of switching signals can be output in a certain "unit time". Traditionally, short messages are called "di" and long signals are called "da". In this way, several signals composed of "di-da" are called "codes", and then they are composed of specified codes, which are transmitted to the air by carriers and then translated into messages by receivers, thus completing the sending process of telegrams. For example, the s in the code corresponds to "di, di, di"; O corresponds to "click, click, click" in the code, so the code of international SOS is "click-click-click-click". From transmission to reception, the speed of telegraph is theoretically the same as that of electricity, and the main time is delayed when calling the receiver and translating the information.

Now it is rarely used for "civil use" because it is not popular.

Telegraph registration used to refer to a communication method similar to "registered letter".

I seem to remember that the previous telegram was 7 cents a word, and the urgent telegram was 0. 14 yuan. This high price is due to the underdeveloped communication in the past, and this kind of telegraph communication needs manual intervention.