When there are many water droplets in the air, the white light of the sun shines on the water droplets and refracts and reflects, resulting in a rainbow. The seven colors of white light have different degrees of refraction, with violet light being the largest and red light the smallest. There are seven colors of Hongqiao in the sky. In this way, the rainbow is the biggest dispersion phenomenon in nature. No matter at home or abroad, the study of dispersion always begins with rainbow.
First, the ancient people's observation of the rainbow has always been a sharp struggle between the understanding of the rainbow, science and superstition. Superstition paints the rainbow with mysterious colors, saying that it is a beauty, a slutty spirit, a bow, and even an animal that can drink water to keep out the rain. Its appearance symbolizes disaster and so on. These are the results of people's low level of understanding and inability to explain natural phenomena.
On the other hand, the working people have observed and explored its laws for a long time and constantly revealed its essence. In China, rainbows were recorded in Oracle Bone Inscriptions of Yin Ruins.
In the first half of the Zhou dynasty, that is, BC 1066-403, the working people in our country had an experience: when the sun rises in the morning, if a rainbow appears in the west, it will rain. They also wrote this experience into poetry: Face west and worship the rain. ? It is recorded in the Songs of the South during the Warring States Period that what is the color of the rainbow? Five colors? . Cai Yong of the Eastern Han Dynasty also talked about the formation conditions and the position rules of the rainbow in his book "Zhang Sentences in the Moon". He said: rainbows are produced in the clouds opposite the sun. You can't see a rainbow without clouds, but it won't form in cloudy weather.
Although these statements are superficial, they are basically correct. In the pre-Qin period, some people tried to explain the formation of rainbow with the philosophical theory of Yin and Yang at that time.
Second, the ancients explained the conditions of rainbow formation. "Zhuangzi" said: More yang and more yin are the rainbow. ? As we know, the formation conditions of rainbows are sunlight and water droplets. In the theory of Yin and Yang, the sun belongs to Yang and the water belongs to Yin. The sun shines on the water droplets. Yang and Yin? , is able to justify. Of course, this does not talk about the nature of dispersion. However, we can also see that the ancients had a unique way of thinking about scientific issues.
By the Tang Dynasty, people's understanding of rainbows had made great progress. It was known at that time that raindrops were produced by sunlight. Kong (A.D. 574-648) wrote in Notes to the Book of Rites that this is arranged in monthly order? Rainbow first seen? The article records below: If the clouds are thin, if the sun leaks, the raindrops in the sun are rainbows. ? The origin of the rainbow has been roughly revealed here. Of course, compared with the modern rigorous and complete explanation, there is still a long way to go. However, it is enough to put forward such an explanation more than 300 years ago.
In Europe, British scientist Bacon (A.D. 12 14- 1294) first discovered that raindrops reflected the sun, which was more than 600 years later than China. As for a more rigorous explanation, it was not put forward until the seventeenth century.
Third, the ancients? Artificial rainbow? In particular, our ancestors not only explained the origin of the rainbow, but also created a rainbow? Artificial rainbow? Experiment. We know that when the mountain is covered with water, water drops splash and the sun shines, it becomes colorful, just like a rainbow, and it is easy to be found. Zhang Jiuling, a poet in the early Tang Dynasty, wrote the poem "Lushan Waterfall at Wanghukou". Is the sunshine like a rainbow? Sentence. Inspired by this phenomenon, people want to know whether it can artificially create the rainbow width.
Recorded in Xuanzhenzi written by Zhang in Tang Dynasty? Spray water into a rainbow on the back of the sky? . You can see the rainbow phenomenon by spraying water into the air with your back to the sun.
This experiment is really meaningful. This is a white light dispersion experiment that people consciously carry out. It directly simulates the rainbow phenomenon, which can not only verify the explanation of the origin of the rainbow, but also give a devastating blow to all kinds of superstitions and heresies about the rainbow in history.
People have been doing this experiment since the Tang Dynasty. For example, in the Song Dynasty, when explaining Mao's poems, it was recorded that: Looking at the water from the side, is it a rainbow? . Here? From the side? It does point out the main points of observation, which is very correct.
Fourthly, other dispersion phenomena observed by the ancients, besides rainbows, also have many dispersion phenomena, which were constantly discovered and recorded around the Tang and Song Dynasties. This not only enriches people's understanding of dispersion, but also helps to explain the cause of rainbow.
First of all, people have deeply observed the dispersion phenomenon of a single water drop. Cheng Dachang of the Southern Song Dynasty recorded a very interesting phenomenon in his book Yan Luzi. He said:
Where the rain falls at the beginning, or the dew is not covered, the rest is dotted at the ends of plant branches and leaves, and they all gather into points when they want to fall. The light is bright and gratifying, the sun enters, and the five colors are full and flickering. It is the sun's light that colors the water, not the rain and dew. ?
That is to say, when the rain clears or the dew is not dry, the water droplets living at the ends of branches and plants will always form shiny water droplets due to the surface tension. Careful observation of one of the small water polo, under the irradiation of sunlight, can present colorful, which is the dispersion phenomenon of white light after refraction and reflection by water droplets.
It is rare for Cheng Dachang to observe this phenomenon carefully and deeply. More importantly, his conclusions are very scientific. He said that this color is not owned by the water droplets themselves, but? Is the sun's light colored in water? . This points out that sunlight contains several colors of light, which can be expressed by the action of water droplets. This can be said to touch the essence of dispersion.
It should be pointed out that understanding the dispersion phenomenon of a single water droplet provides a more solid foundation for explaining the phenomenon that water droplets reflect the sun and become rainbows, and its significance is obviously enormous.
On the other hand, the dispersion of some crystals has been found in China since the Southern and Northern Dynasties. At that time, a transparent rock crystal was recorded in The Golden House, which was called Bi Salt or Yuhua Salt. And its reflection on the sun, as light as amber? . ? Amber. Colors are red, yellow and brown, that is to say, white light presents several colors after refraction by crystals. This is the earliest record of crystal dispersion.
Later, more people recorded this phenomenon. What? Bodhisattva stone? 、? Sharping stone? Wait, can you tell? Japan and China shine with five colors? Phenomenon; Some even write directly? Sunlight turns into five colors, like a rainbow. ?
But before the Northern Song Dynasty, we didn't know much about this phenomenon, so there were some unrealistic statements, such as Yang Yi in the Northern Song Dynasty, which recorded Mount Emei. Bodhisattva stone? ,? How many colors does the sun have? The phenomenon is correct; On the other hand, I think it's because Emei Mountain has? Buddha light? The relationship between, this is wrong. Cheng Dachang of the Southern Song Dynasty criticized this mistake. What is his basis? These five colors can't be seen every day? The fact of this decision? Not because of the Buddha in Emei? . In his view, the role of bodhisattva stone is the same as that of small water drops. Is it the same? Is the light of the sun colored? Result. This is the correct explanation.
As can be seen from the above brief introduction, in ancient China, we had a deep understanding of the chromatic dispersion of rainbows, and we also found many chromatic dispersion phenomena. Fang Yizhi, a scientist in Ming Dynasty, made a brief record of this knowledge in Introduction to Physics. He said:
Gemstones glow where they are raised, with several edges and five colors on one side. For example, sparkling stone, six sides, water products pressing paper, three sides, burning materials and water products are also five colors; The canyon shot the flying spring into five colors; People spray water on the sun between the back walls, which is also colorful. Therefore, we know that the color of the rainbow, the green of the stars and the moon, and the five-color clouds are all the same. ?
He not only comprehensively listed all kinds of dispersion phenomena, including the dispersion of rock crystal (Emei sparkling stone), the dispersion of artificial transparent body (crystal paper burning crystal) and the dispersion of water droplets (canyon solar jet flying spring, spraying water on the sun); More importantly, it can be pointed out that the rainbow phenomenon, like the halo and clouds of the sun and moon, is the dispersion of white light.
Verb (abbreviation of verb) After the middle of Ming Dynasty, China's research on dispersion was gradually introduced from western modern science. For example, Italian missionary Matteo Ricci (1552- 16 10) came to China with a prism and gave a dispersion performance. Later, some China scholars tried to translate foreign natural science works, including spreading knowledge. However, those introductions are often not very correct. Even the discussion on dispersion in the book Yu Gong in the Mirror written by Zheng, a scientist in Qing Dynasty, is not clear.
China was the first to introduce modern dispersion knowledge correctly by Zhang Fuxi (? -1862) translated the theory of light (1853). This book expounds the splitting, refraction, light synthesis and color wheel of prism, and explains the cause of rainbow through the refraction and reflection of white light in water droplets. The book also takes the rainbow as an example to prove that white light can be divided into seven colors. In this way, people's scattered knowledge is more complete.