On what principle did people invent the stethoscope?

The principle of stethoscope listening is very simple. What participates in the aluminum film of stethoscope is the vibration conduction between substances. The two earphones, the induction cavity head of the stethoscope and the pipes connected with them are all hollow. After the film on the surface of the sensor head contacts the human body, the sound becomes mechanical vibration, which can be transmitted to the doctor's ear without external interference through the air in the closed space, and the doctor can clearly hear the sound in the patient's body.

Answer supplement

Comparing the two, I think it is a message. Although mechanical waves can be said to carry mechanical energy, they are somewhat reluctant to this problem. Finally, doctors can use stethoscopes, or just receive information for reference only ~ ~