He said in "Spring and Autumn Stories Similar to Motion": "Objects with the same nature can sense each other, and drums and gongs move because they have the same tone. This is an inevitable phenomenon, and there is nothing magical. "
It is a contribution that Dong Zhongshu can correctly realize that this is a natural phenomenon and break the mysterious atmosphere hanging over it. In the Song Dynasty, the scientist Shen Kuo further promoted the ancient people's research on resonance phenomenon. He explored the resonance of musical instruments by experiment.
He cut a small paper man, put it on the pitch string, dialed the corresponding overtone string, and the paper man jumped and played other strings, but the paper man did not move. In this way, he intuitively demonstrated the resonance phenomenon of two strings when the pitch difference is eight degrees by experiment.
Shen Kuo's experiment, compared with similar experiments in Europe, is centuries earlier. Shen Kuo's experiment had a great influence on later generations. Fang Yizhi, a scholar in the late Ming Dynasty, clearly summarized in his Introduction to Physics that the sum of sounds is enough to feel different. As long as the sound characteristics are consistent, that is, the same frequency or a simple integer ratio, it can also resonate on different objects. He pointed out that the resonance of musical instruments has the same essence, which is caused by "harmony of sound". Fang Yizhi's words marked a further step in people's understanding of the essence of resonance phenomenon. In fact, the ancients' initial understanding of resonance phenomenon and its gradual deepening were accompanied by their understanding of waves in nature. In other words, resonance is closely related to waves in nature.
In ancient times, people often saw such a phenomenon in fishing and hunting production: ripples of water waves in lakes and ponds, duckweed and wooden strips on the water surface do not move with the waves, but vibrate up and down; In spinning rope netting, the rope is bounced and the waves pass from one end to the other, but the thread on the rope does not go with the flow. For similar phenomena, people have been thinking for a long time before they have an answer. As Guanxia said: The ebb and flow of the tide is an inevitable trend. This is the answer of people in the Spring and Autumn Period.
By the Eastern Han Dynasty, people had a further understanding of this. Wang Chong, a thinker in the Eastern Han Dynasty, finally discovered that the propagation form of sound in the air is the same as that of water waves.
Wang Chong said in Lun Heng Cheng Xu: A fish is one foot long and moves in the water, and the water next to it will not exceed several feet. It is as big as a human being, and its swinging distance is only a hundred steps, but it is still safe and clear from a mile away because it is too far away.
If people's good and evil behavior can change Qi, then its distance should be equal to the distance that fish shakes water, and the range of good and evil behavior of Qi should be the same as that of water.
Wang Chong expressed a scientific idea here: the intensity of waves decreases with the increase of propagation distance. For example, the water waves stirred by fish disappear 500 meters away without taking more than 100 steps; The air waves aroused by people's words and deeds, like the water waves aroused by fish, also decays with distance.
It can be considered that Wang Chong is the first person in the world to show people invisible sound wave pictures, and also the first person to point out the relationship between sound intensity and propagation distance. In the Ming dynasty, the idea of comparing sound waves in the air with water waves became clearer and clearer. Song, a scientist in the Ming Dynasty, concluded in On the Sound of Qi that when a stone falls on the water, hitting the object will make the air fluctuate, just like waves. Sound wave is longitudinal wave, and the direction of its propagation energy is parallel to the direction of vibration; Water wave is a shear wave, and its energy transmission direction is perpendicular to the vibration direction. Although the ancients could not distinguish longitudinal waves from transverse waves because of the limitations of the times, the above understanding was a great progress in acoustics.
Dong Zhongshu