A brief history of telescopes
One day in the early 17th century, Kobisch, the owner of an optical shop in the town of Mittelburg in the Netherlands, in order to check the quality of the ground lenses, he put a convex lens Line up a line with a concave mirror, look through the lens, and find that the church tower in the distance seems to become larger and closer, so I accidentally discovered the principle of the telescope. In 1608, he applied for a patent for the telescope he made and complied with the authorities' request to build a pair of binoculars. It is said that dozens of opticians in the town of Mittelburg claimed to have invented the telescope, but Liebich is generally believed to be the inventor of the telescope.
The news of the invention of the telescope quickly spread throughout Europe. After the Italian scientist Galileo heard the news, he made one. The first telescopes could only magnify objects 3 times. A month later, the second telescope he built could magnify 8 times, and the third telescope could magnify 20 times. In October 1609, he built a telescope that could magnify 30 times.
Galileo used a homemade telescope to observe the night sky and discovered for the first time that the moon's surface was rugged, covered with mountains and had cracks in craters. After that, he discovered the four satellites of Jupiter and the sunspot movement of the sun, and concluded that the sun is rotating.
Almost at the same time, the German astronomer Kepler also began to study telescopes. He proposed another astronomical telescope in "Diopters". This telescope consisted of two convex lenses, which was different from Galileo's telescope. , with a wider field of view than the Galilean telescope. But Kepler did not build the telescope he described. Scheiner first made this kind of telescope between 1613 and 1617. He also followed Kepler's suggestion and made a telescope with a third convex lens, turning the inverted image of the telescope made of two convex lenses into an upright image. . Scheiner built 8 telescopes and observed the sun one by one. No matter which one, he could see the same shape of sunspots. Therefore, he dispelled many people's illusion that sunspots may be caused by dust on the lens, and proved that sunspots are indeed observed. Scheiner installed special light-shielding glass when observing the sun, but Galileo did not add this protective device. As a result, he injured his eyes and was almost blind in the end.
In order to improve the accuracy of the telescope, Huygens of the Netherlands built a telescope with a barrel length of nearly 6 meters in 1665 to detect the rings of Saturn, and later built a telescope with a length of nearly 41 meters. .
A telescope that uses an objective lens and an eyepiece is called a refracting telescope. Even if the lens tube is lengthened and the lens is precisely processed, chromatic aberration cannot be eliminated. In 1668, British scientists solved the problem of chromatic aberration with the reflective telescope. The first anti-telescope was very small. The diameter of the mirror in the telescope was only 2.5 centimeters, but it could already clearly see the moons of Jupiter and the phases of Venus. In 1672, Newton built a larger reflecting telescope and gave it to the Royal Society. It is still kept in the library of the Royal Society.
Newton once believed that chromatic aberration was irredeemable, but later proved to be too pessimistic. In 1733, the Englishman Hal made an achromatic refracting telescope. In 1758, Paul Land of London also made the same telescope. He used glass with different refractive principles to make convex lenses and concave lenses respectively, and the colored edges formed by them canceled each other out.
But it is not easy to make a very large lens. Currently, the largest refracting telescope in the world has a diameter of 102 centimeters and is installed at the Ardis Observatory.
Reflecting telescopes developed rapidly in astronomical observation. In 1793, Hessel in the United Kingdom made a reflecting telescope. The reflector was 130 meters in diameter, made of copper-tin alloy, and weighed 1 ton. The reflecting telescope made by Lowes in England in 1845 had a reflector diameter of 1.82 meters. Counter telescope at Mount Wilson Observatory in 1913, 254 meters in diameter. In 1950, a reflecting telescope with a 5.08-meter diameter mirror was installed on Mount Palomar. In 1969, a 6-meter-diameter reflector was installed on Mount Pastukhov in the northern Caucasus of the Soviet Union. It was the largest reflecting telescope in the world at that time. Most large observatories now use reflecting telescopes.
The history of generators
In the early 19th century, an important topic studied by scientists was the method of obtaining electric energy cheaply and conveniently.
In 1820, after Oersted successfully completed an experiment in which an energized wire could deflect a magnetic needle, many scientists at that time conducted further research: the deflection of the magnetic needle was due to the action of force. This mechanical Force, the electric force that comes from the flow of electric charges. So, can mechanical force be converted into electricity through magnetism? The famous scientist Ampere was one of these researchers. He experimented with many methods, but he made fundamental mistakes and the experiment was not successful.
Another scientist, Colaton, conducted such an experiment in 1825: inserting a magnet into a cylindrical coil, he thought that this might be able to obtain an electric current. In order to prevent the magnet from affecting the ammeter that detects current, he used a long wire to connect the ammeter to the next room. He had no assistant, so he had to insert the magnet into the coil and then run to the next room to see if the ammeter pointer deflected. Now it seems that his device is completely correct and the experimental method is correct. However, he made a really regrettable mistake. This is the deflection of the meter pointer, which only occurs at the moment when the magnet is inserted into the coil. After the magnet is inserted into the coil, it does not move, and the meter pointer returns to its original position. So, after he inserted the magnet, he quickly ran to the next room to look at the meter. No matter how fast he ran, he could not see the deflection of the meter pointer. If he had an assistant, if he had put the electric meter in the same room, he would have been the first person to achieve the conversion of mechanical force into electricity. However, he lost this good opportunity.
Another six years passed, and on August 29, 1831, the American scientist Faraday succeeded in converting mechanical force into electricity. His experimental device was no different from Colaton's, except that he placed the ammeter next to him, and the moment the magnet was inserted into the coil, the pointer deflected obviously. He succeeded. The mechanical force of the hand that moves the magnet is finally transformed into the electrical force that moves the charge.
Faraday took the most difficult step. He continued to research, and two months later, he trial-produced the first real generator that could produce a steady current. It marked the transition of mankind from the steam age to the electrical age.
Over the past 100 years, many modern forms of power generation have appeared, including wind power generation, hydropower generation, thermal power generation, atomic power generation, thermal power generation, tidal power generation, etc. The structure of the generator is becoming more and more perfect. The efficiency is getting higher and higher, but the basic principle is still the same as Faraday's experiment: a moving closed conductor and a magnet are indispensable.
The invention of nuclear magnetic spectrometer
Nuclear magnetic spectrometer is widely used in the research of organic substances, chemical reaction kinetics, polymer chemistry, as well as medicine, pharmacy and biology. fields of study. Over the past 20 years, due to the rapid development of this technology, it has become one of the most important analytical technologies in the field of chemistry.
As early as 1924, the Austrian physicist Pauli proposed that some nuclei may have spin and magnetic moment. The word "spin" originates from the classic image of charged particles, such as protons and electrons, rotating around their own axis. This motion must produce angular momentum and magnetic dipole moment, because the rotating charge is equivalent to a current coil, and it is known from classical electromagnetic theory that they produce a magnetic field. Of course, this explanation is just a vivid comparison, and the actual situation is much more complicated than this.
The spin of the atomic nucleus can be expressed by the spin quantum number I. Spin quantum is obtained, and there is the following relationship between the mass number and the atomic number:
Mass number atomic number Spin quantum number (I)
Odd number odd number or even number 1/2, 3 /2, 5/2...
Even even number 0
Even odd number 1, 2, 3...
1gt; 0 nucleus spins A magnetic field will be generated; for a nucleus with I 1/2, its charge distribution is spherical; while for a nucleus with I ≥ 1, its charge distribution is not spherical, so it has a magnetic pole moment.
The atomic nucleus with I = 0 is placed in a strong magnetic field. Under the action of the strong magnetic field, the energy level will split. If electromagnetic radiation with a frequency suitable for its energy level is used, it will Vibration absorption occurs, from which the name NMR comes.
Stern and Gerlacher observed the magnetic deflection of lithium atoms and silver atoms in atomic beam experiments in 1924, and measured the atomic magnetic moment caused by unpaired electrons.
In 1933, Stern and others measured the magnetic moment of the proton. In 1939, Bila conducted the first NMR experiment. In 1946, Pusier and Bushoch of the United States simultaneously proposed an experimental report on proton NMR. They first used NMR methods to study the properties of solid matter, atomic nuclei, and the energy exchange between atomic nuclei and the environment around the nuclei. etc. questions. For this they both won the 1952 Nobel Prize in Physics. In the 1950s, the nuclear magnetic resonance method began to be used in the field of chemistry. In 1950, two physicists at Stanford University, Proctor and Yu, used NH 4NO3 aqueous solution as the source of nitrogen nuclei. When measuring the magnetic moment of 14N, they discovered two properties Completely different vibration signals, thus discovering that the same atomic nucleus can absorb energy in different vibration conditions depending on its chemical environment, that is, the nuclear magnetic resonance frequencies are different. This phenomenon is called "chemical shift". This is due to the interaction between the magnetic field formed by the electrons outside the nucleus and the external magnetic field. Chemical shift is an important basis for identifying functional groups. Because the size of the chemical shift is closely related to the nature of the bond and the type of bonded elements. In addition, the magnetic interaction between each group of atomic nuclei constitutes spin-spin coupling. This effect often causes groups of nuclei with different chemical shifts to display not a single peak but multiple peaks on the vibrational absorption diagram. This situation is determined by the number of adjacent nuclei in the molecule, distance, symmetry and other factors. So it helps tip the whole molecule.
As a result of the above results, the high-resolution nuclear magnetic resonance instrument was born. The nuclei measured at the beginning are mainly hydrogen nuclei, which is due to its strong NMR signal. As the performance of the instrument improves, 13C, 31P, 15N and other nuclei can also be measured, and the magnetic field used by the instrument becomes stronger and stronger. In the 1950s, the IT (Truss) magnetic field was created, and in the 1960s, the 2T magnetic field was created, and the induction phenomenon was used to create a 5T induction magnet. An 8T magnetic field was created in the 1970s. NMR spectroscopy has now been applied to a variety of chemical systems ranging from small molecules to proteins and nucleic acids.
The invention of the emission spectrometer
The famous British scientist Newton used a prism to observe the spectrum in 1666, which can be said to be the earliest spectroscopic experiment. Since then, many scientists have engaged in spectroscopy research. In 1800, the British astronomer Herschel measured the thermal effects of various parts of the solar spectrum and discovered infrared rays for the first time in the world. In 1801 Ritter discovered ultraviolet light. In 1802, Wollaston observed the discontinuity of the solar spectrum and found that there were many black lines in the middle. This was originally a very important discovery, but he mistakenly thought it was the dividing line of colors. In 1803, British physicist Thomas Young conducted an experiment on light interference, which provided the first method to measure wavelength.
The German physicist Fraunhofer rediscovered and compiled the solar spectrum, which contains many black lines (more than 700), and the important black lines are labeled from A to H Marked with equal letters (known as "Fraunhofer lines"), these black lines later became the standard for comparing the dispersion rates of different glass materials. These results were published one after another between 1814 and 1815. Fraunhofer also invented the diffraction grating. At first, he wrapped silver wire around two screw rods to make a grating. Later, he built a notching machine and used diamond to score the glass to make a transmission grating.
The applied research of spectral analysis began with Kirchhoff and Bunsen. Bunsen was a professor of chemistry in Hamburg, Germany. He invented the Bunsen burner and studied the changes of various substances in high-temperature flames. Kirchhoff was a physics professor in Hamburg and was familiar with optics. The two of them collaborated to create the first shuttle spectroscope (spectroscope).
This instrument uses the technology pioneered by Newton in 1666, which allows light to pass through a prism and unfold into a rainbow light band (spectrum). They used a lens to integrate the light emitted by the substance when it burned in a Bunsen burner into a beam of parallel light, passed it through a narrow slit, and then through a prism, and used a telescope to amplify the resulting spectrum.
Kirchhoff and Bunsen discovered that the flame emitted by each chemical element when burning has a unique color and can be identified accordingly. In 1860 and 1861 they discovered cesium and rubidium using a spectrometer. After that, with the help of spectral analysis method, we found that many elements on the earth are also found in the sun. In 1868, the French astronomer Janssen and the British astronomer Rockyer respectively used spectroscopic methods to discover an element that had not been discovered on the earth at that time. They believed that it was a unique element in the solar atmosphere and named it helium, which means "sun" meaning. In this way, spectroscopic methods have also been applied to astronomy.
With the rapid development of spectral method research, new problems have also emerged. One of the main problems is the lack of wavelength standards with sufficient accuracy, resulting in chaotic observation results and the inability to communicate with each other.
In 1868, Estrang published the "Standard Solar Spectrum" chart, recording the small wavelengths of thousands of Fraunhofer lines, in units of 10-8 centimeters, and accurate to 6 digits, as The spectroscopy workers provided extremely useful information. To commemorate him, 10-8 centimeters later became known as the Angstrom unit, abbreviated as Angstrom (A). It was replaced by the more accurate Roland data sheet more than ten years later.
Modern spectrometers do not use prisms but use diffraction gratings. This is a plate with thousands of lines engraved on it, which separates the light, and then the spectrum is photographed or recorded, and then analyzed using electronic instruments.
Spectrometers are widely used in metallurgy, geology, environment and other fields.
History of Lightning Rods
1. Lightning rods are first of all lightning protection devices manufactured and used by the working people of our country. Some say that Czech priest Prokop Divi? installed the first lightning rod in 1754. More people believe that Franklin of the United States made the world's first lightning rod in 1753. In fact, our country had already manufactured and first used lightning rods before 1688.
As early as the Three Kingdoms period (220 to 280 AD) and the Southern and Northern Dynasties period (420 to 581 AD), there are records of "lightning protection rooms" in ancient Chinese books. According to records in "Millet" written by Wang Rui of the Tang Dynasty, during the Han Dynasty (206 BC to 220 AD) in my country, someone proposed that making tiles into a fishtail shape and placing them on the roof could prevent fires caused by lightning. Lightning protection devices have also been found on some ancient buildings in our country. After the French traveler Cabriolet Demagalin traveled to China, he wrote this record in his book "News in China" in 1688: " At that time, there was an upturned dragon head on both sides of the roof of the new house in China. The dragon's mouth spit out a twisting metal tongue, reaching into the sky. The tongue was connected to thin wires, which went straight to the ground. This wonderful device was causing thunder and lightning. If lightning strikes the house, the current will flow down from the dragon's mouth to the ground without any destructive effect. "It can be seen that the world's first lightning rod was created by the intelligent working people of our country. manufactured.
2. The development of lightning rods. Today, safer lightning rods have been discovered in the world. The safer lightning rod is no longer needle-shaped, but like a feather duster. This lightning rod was invented by two Americans. According to a recent report by the New York Times, the center of this lightning rod is a tube, and 2,000 thin wires are drawn from the top, and these wires are distributed in a radial pattern. This method better dissipates the static charge that collects around the building.
3. "Lightning rod is outdated." At present, our country has successfully developed a semiconductor lightning arrester. Its lightning protection effect far exceeds that of lightning rods and also far exceeds similar products produced in the United States, France, and Australia. The semiconductor lightning arrester has two major functions: (1) When a strong thundercloud appears over a building, it emits a 1-meter-long corona spark to neutralize the sky current and reduce lightning strikes; (2) In the event of a lightning strike, the relevant devices on the semiconductor lightning arrester can block the strong current released by the lightning strike.
Xie Guangrun, a professor at Wuhan Institute of Water Conservancy, a well-known lightning protection expert in my country, suggested installing this kind of semiconductor lightning arrester on tall buildings to protect national property. Xie Guangrun said that my country has now installed semiconductor lightning arresters in 24 units in strong minefields. After several years of testing, it has been proven that it can indeed save buildings from danger time and time again. He called on relevant units, especially the departments of national defense engineering, meteorology, electric power, communications and broadcasting, to promote semiconductor lightning arresters as soon as possible to reduce lightning strikes.
Was the bicycle invented by the Chinese?
There are many theories about the invention of the bicycle.
① my country is the first country in the world to invent bicycles. The ancestor of the bicycle is the unicycle in my country more than 500 BC. During the Kangxi period of the Qing Dynasty (1662-1722), Huangluzhuang invented the bicycle. Volume 11 of "Unofficial History of the Qing Dynasty" contains: "A two-wheeled cart made by Huangluzhuang is more than three feet long and can seat one person. It does not need to be pushed or pulled, and can move on its own. When traveling, use the hand to turn the axis and turn it around. Traveling as before, staying and moving for eighty miles. "This is the earliest bicycle in the world.
②The bicycle was invented by Western Europeans. In 1790 AD, the Frenchman Sifulak developed a wooden bicycle without handlebars, pedals, or chains. The shape of the car is like a wooden horse, with two wheels nailed to its feet, and the two wheels are fixed in a line. Since the bicycle had no driving device or steering device and the seat was low, Sifulak rode on the bicycle by himself, put his feet on the ground, and pushed backwards hard to make the bicycle move forward in a straight line. In 1817, Baron von Drais of Germany invented a handlebar that could move freely, making it easier to change his bicycle. In 1818, Delais applied for a patent in England. In 1839, K. Macmillan, a British worker, pioneered a pedal bicycle that used a crankshaft mechanism to drive the rear wheel, allowing people to lift their feet off the ground while riding a bicycle. One day in 1861, Parisian carriage and stroller manufacturers Michaud and his sons were repairing a Delais-style bicycle. After repairing it, when they tried it on a ramp, they found that it was difficult to put their feet on the bicycle, so they improved it. A pedal crankshaft was installed on the front wheel, thus creating the Michaud bicycle, which soon began to be mass-produced. Around 1870, France's Ma Zhi made another bicycle with a large driving wheel at the front and a small driven wheel at the back. This kind of bicycle had better operating results. After 1890, the British Humber Company produced a chain-driven, diamond-shaped bicycle. This form of bicycle is still in use today.
③The bicycle was invented by the Russians. One day in September 1801, the Russian serf Artamonov rode a wooden bicycle he made and traveled 2,500 kilometers to Moscow to present a gift to Tsar Alexander I. The bicycles made by Artamonov are similar to those made by the Frenchman Sifulak. When Alexander I saw the bicycle made by Artamonov, he immediately ordered that his slave status be cancelled.
Optical knowledge in ancient my country
The origin of optics, like mechanics and thermal science, can be traced back to two or three thousand years ago. Our country's "Mo Jing" records many optical phenomena, such as projection, pinhole imaging, plane mirrors, convex mirrors, concave mirrors, etc. The West has also recorded optical knowledge very early. Euclid (about 330-260 BC) studied the reflection of light in "Catoptrica". The Arab scholar Al-Hazen , 965~1038) wrote a "Encyclopedia of Optics", which discussed many optical phenomena. The true formation of optics as a science should be counted from the era when the laws of reflection and refraction were established. These two laws laid the foundation of geometric optics. The nature of light is also an important topic in optical research. The particle theory regards light as consisting of particles, and believes that these particles fly in straight lines according to mechanical laws, so light has the property of linear propagation. Before the 19th century, the particle theory was relatively popular. However, with the deepening of optical research, people have discovered many phenomena that cannot be explained by rectilinearity, such as interference, diffraction, etc., which can be easily explained by the wave nature of light, so the wave theory of light has prevailed again. The debate between the two theories constitutes a red line in the history of optical development.
1. Methods of making fire and understanding of fire
The tool for making fire in ancient my country is called "suil", which can be divided into gold and wood. The golden sui draws fire from the sun, and the wooden sui draws fire from wood. According to records in ancient Chinese books, "Fu Sui" and "Yang Sui" (actually a concave mirror, collectively called "Jin Sui" because it is made of metal) were commonly used in ancient times to make fire. In ancient times, people always carried firearms with them when marching or hunting. In the "Book of Rites", there are records of "wearing a golden flint on the left" and "wearing a wooden flint on the right", indicating that golden flints were used to make fire on sunny days and on cloudy days. Use wood to make fire. Yangsui fire-making is a pioneer in mankind's use of optical instruments to concentrate solar energy. Speaking of making fire, homemade ancient lenses were used to make fire in ancient times. In the 2nd century BC, some people used ice as lenses to focus sunlight to make fire. There are such records in "Wenjingtang Series" and "Huainan Wanbi Shu": "Peel the ice to make it round, hold it toward the sun, and use moxa to support its shadow, then fire will be born." We often say that water and fire are incompatible. But making an ice lens to capture fire is a wonderful creation. Lenses made of ice cannot be stored for a long time, so lenses made of glass or glass appeared.
2. Understanding of pinhole imaging and shadow
In the 4th century BC, Mohists conducted experiments on pinhole imaging and provided analysis and explanations. "Mo Jing" clearly writes: "When the scene reaches (inverted), it has an end at noon, and when the scene is long, it is said to be at the end." The "noon" here is where the small hole is. This text shows that the small hole creates an inverted image. The reason is that there is a point ("end") where the light rays intersect at the small hole. The size of the image has nothing to do with the position of this intersection point. It can also be clearly seen from here that the ancients have realized that light travels in a straight line, so "shoot" is often used to describe light going straight forward. Shen Kuo of the Northern Song Dynasty also described experiments on linear propagation of light and small hole imaging in "Mengxi Bi Tan". He first directly observed the shadow flying in the air, and the shadow on the ground also moved in the same direction as the flying direction. Then a small hole was opened in the paper window so that the shadow flying outside the window would appear on the paper screen inside. Shen Kuo used the principle of straight forward light to explain the observed results: "The east will shadow the west, and the west will shadow." East". Mohists took advantage of the linear propagation property of light to discuss the relationship between light source, object, and projection. "Mo Jing" writes: "The scenery does not move, it is said that it is changing." "When the light arrives, the scenery dies. If it is there, it will cease to exist." It means that the shadow is immovable. If the shadow moves, it is a light source or object. Movement occurs, so that the original shadow continues to disappear and new shadows are constantly generated. If light shines on the projection place, the shadow will disappear. If the shadow exists, it means that the object is not moving. As long as the object is not moving, the shadow will always exist in the same place. The Mohists also explained the umbra and penumbra. There is such a record in "Mo Jing": "Scene 2, it is important to talk about it." "Scene 2, light clip. One, light one. The light is the scene." It means that one object has two projections (umbral, half shadow) Shadow), indicating that it is the result of repeated illumination by two light sources at the same time ("Said Being", "Light Clamp"), a kind of projection, indicating that it is illuminated by only one light source, and emphasizing the connection between the light source and the projection ("Light Clip") The person is the scenery"). Connected with this, Mohists also discussed the size of shadow and its changes based on the changes in the relative positions of the object and the light source, as well as the differences in the sizes of the object and the light source themselves.
3. Understanding of opposite mirrors
The Mohists made in-depth observations and research on concave mirrors, and made clear and detailed records in the "Mo Jing". "Jian low, the scene is small and easy, and the scene is large and upright. It is said to be outside and inside the middle." "Low" means deep and concave; when placed "inside the middle", the image obtained is larger and larger than the object. Upright. Shen Kuo of the Northern Song Dynasty measured the focal length of a concave mirror. He placed his fingers in front of a concave mirror to observe the image, and found that as the distance between his fingers and the mirror changed, the image also changed accordingly. It is recorded in "Mengxi Bi Tan": "If the Yang Sui face is depressed, press it with one finger and it will be upright. As it gets further and further away, you will not see anything. After this, it will fall." This shows that when the finger is close to the concave mirror, the image will be upright. , gradually moves away to a certain place (near the focus), then "nothing is seen", which means there is no image (the image is at infinity); after moving this distance, the image becomes upside down. This experiment not only describes the imaging principle of a concave mirror, but is also a rough method for measuring the focal length of a concave mirror.
The Mohists also studied convex lenses.
"Mo Jing" writes: "Jian Tuan, Jing Yi. It is said that the punishment is great." "Jian Tuan" is the Yan-mian mirror, also known as the Tuan Mirror. "Scene 1" indicates that there is only one image formed by a convex mirror. "Xing" has the same shape as an object, and it is always bigger than an image. Our ancestors took advantage of the ability of plane mirrors to reflect light and combined multiple plane mirrors to achieve interesting results. For example, this is recorded in the "Zhuangzi Supplement", a relevant comment on "Zhuangzi Tianxia Chapter": "The mirror is used to identify the shadow, and the mirror is to have a shadow. If the two mirrors reflect each other, there will be endless double images." Such a device has received The effect of "looking at flowers in the front and rear mirrors, flowers reflecting each other". "Jianjingtang Series" and "Huainan Wanbi Shu" record that "take a large mirror and hang it high, put a basin under it, and you can see all around." This shows that someone made the earliest open-tube "periscope" very early ", you can watch the outdoor scenery through the wall.
4. Understanding the rainbow
The rainbow is an atmospheric optical phenomenon. Starting from the 6th century AD, ancient my country had a relatively correct understanding of the rainbow. Kong Yingda (574-648) in the early Tang Dynasty once summarized the cause of the rainbow. He believed that "if the clouds are thin and the sun is missing, the sun will shine on the raindrops, and the rainbow will appear." He clearly pointed out the three conditions for the formation of a rainbow, namely clouds, the sun, and "sunlight on the raindrops." . Shen Kuo also made detailed research on this and conducted on-site inspections. In "Selected Notes on Mengxi's Bi Tan", he wrote: "It was a new rain, and I saw a rainbow hanging down in the stream in front of the tent." I and my colleagues looked at it, and saw that both ends of the rainbow were hanging down in the stream. When people are crossing a stream, they are facing each other across a rainbow, several feet away from each other. The middle is like a bamboo shoot, and when looking from the west to the east, they can see a rainbow. If you look east and west of the stream, you will see nothing due to the glare of the sun. "Point out that the positions of the rainbow and the sun are exactly opposite. The rainbow in the evening can be seen in the east, but the rainbow cannot be seen facing the sun. After understanding the earth rainbow, we can artificially create a rainbow. In the middle of the 8th century, there was such a rainbow in the Tang Dynasty Experiment: "Spraying water with your back to the sun into a rainbow shape" means spraying small water droplets with your back to the sun, and you can see a rainbow-like scene.
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