According to the theory of human origins on land, the sea is the birthplace of all living things, and humans evolved from lungfish crawling out of the sea in wet strips. The underwater world is actually fascinating and mysterious. There, the sound resonates vividly and the sound seems to come from all directions, making it difficult for people (like divers) to distinguish their direction.
The speed of sound waves traveling through air is approximately 340 meters/second. There is a difference in the time it takes for sound (except from the front and back) to reach both ears. Typically use this momentary time difference to identify the location of the sound. However, the speed of sound propagation in sea water is around 1,500 meters/second, more than 4 times that in air. Therefore, the direction of a certain sound can be discerned in the air (i.e. there is a dperceptible time difference). between the sound reaching both ears), but in sea water. The sound is transmitted to both ears almost at the same time, and the time difference between reaching both ears is so small (less than 1/4 of that in the air) that it is impossible to distinguish it to the human ear. For example, the sound of a steamboat is like the buzzing of a saw in the water to a diver in the ocean. Although it can be heard from afar, it is impossible to determine the steamboat's direction. Sound seems to travel very far in air without many obstacles, but in water it has fewer obstacles and can travel further. However, it is very difficult for sound to travel from air to water. Once it reaches the water surface, only about one ten thousandth of the sound energy is carried by the sound and continues to propagate. Therefore, most sounds from the sea surface do notcannot be heard underwater.
What you can see underwater is a colorful, unpredictable and poetic world. Light moves differently underwater than in air. When a person opens their eyes while swimming, all they see is a chaotic, blurry world. But if you put on a mask, everything that happens underwater becomes clearly visible. Indeed, light waves propagate more slowly underwater than in air and light traveling in water cannot be focused on the retina. There is a layer of fluid in the outermost layer of the human eye. The reason why we can see objects clearly on earth is that the light from the object is refracted by this liquid layer, and then focuses on the retina through the action. other refractive media in the eye. In the water, if you do not wear a mask, your eyes are in direct contact with the sea water. The light passes through the sea water and shines directly on it.ent on the outer layer of our eyes. The degree of refraction is much less rapid and significant. when it moves through the air, causing the light to not shine well on the retina. After wearing a mask, the situation is different: there is a gap between the eyes and the sea water. Light rays enter the air layer of the mask from the water and then enter the eyes. It's almost the same visual process as on the water. land. But here, the light must be refracted twice: once in the mask and once in the human eye. With additional refraction, the object appears closer and larger, about a third larger and about a third closer than before (a refraction). Therefore, a 3 inch long fish becomes 4 inches long and a person four meters away looks the same as if they were standing three meters away.
There are two main types of marine luminescence phenomena:
1. Some marine organisms produce luminescent substances. This is a special type of chemical substance, but this type of luminescence mainly exists in certain fixed parts, such as the head of krill.
2 Some marine organisms do not secrete luminescent substances and their luminescence phenomenon is. caused by It is produced by parasitic or symbiotic luminescent bacteria in its body, and the location of this type of luminescence is not fixed