Have you ever imagined what will happen in the ocean when an earthquake happens underground? If you've ever felt a big earthquake or seen one on television, you know that it has the power to shake the ground and move large buildings. When a great earthquake happens under the ocean floor, the earthquake's large energy is transferred (转移) to the water above it, creating a series of water waves called a tsunami (海啸). The word comes from the Japanese words tsu (harbor) and nami (wave).

Normal ocean waves have an average wavelength (波长) of about 100 meters and an average height of about 2 meters, while a tsunami can have a wavelength of 193 kilometers or more. Travelling at up to about 800 kilometers per hour in the deep ocean, a tsunami might be at a height of as little as 0.9 meters, which makes it almost impossible to be noticed, even for a ship in the area.

As a tsunami approaches (靠近) a coastline, things begin to change greatly. As it approaches shallow (浅的) waters, the wave speed drops below about 80 kilometers per hour. The wavelength also decreases much, but amplitude—the height of the wave—increases greatly, leading to the huge wall of water along coastlines, which causes great damage to coastal areas.

About 80% of tsunamis happen in the Pacific Ocean. Tsunamis cannot be prevented, but areas that experience tsunamis regularly have developed tsunami warning systems to give as much advance warning as possible to people who live along the coastline. For example, there are tsunami warning signs and warning sirens (警报器) atop nearby hills along Japanese coastlines. And many Japanese coastal communities have built tsunami walls, floodgates and others to stop or change the direction of water from incoming tsunamis.

People believe that every word has its correct meaning(s). When we are not sure, we usually check online, or turn to our teachers or dictionaries. But do you know how dictionaries were made in the past? 

Dictionary writers first read the important books of the period or the subject that the dictionary was about. As they read, they copied necessary information on cards: interesting words, common words—both in their daily uses and unusual uses, and also the sentences where they were used. That is to say, the words, along with the uses of each word, were collected. For a really big dictionary, millions of such cards were collected. This task could last for years. As the cards we recollected, they were put in alphabetical order(A—Z). When this was done, there would be several hundred cards for each single word. 

Then, to define(定义)a word, the dictionary writer placed its hundreds of cards before him. He read the cards closely, threw away some, read the rest again, and divided up the cards according to what he thought were the common uses of the word. Finally, he wrote the definitions, following the hard-and-fast rule: each definition must come from an example on a certain card in front of him. 

So, the writing of a dictionary was not a task of inventing meanings of words, but a task of recording their meanings. The writer of a dictionary was a historian, not a law maker. 

As time develops, the way of producing dictionaries has greatly changed. Nowadays, we can use online dictionaries too. When choosing our words in speaking or writing, we can be guided by the dictionary. However, we cannot be controlled by it, because new situations, new experiences, new inventions, and new feelings are always pushing us to give new uses to old words. 

Each year on December 10, the Nobel Foundation (诺贝尔基金会) presents six prizes. These prizes are named after Alfred Nobel, the man who invented dynamite (火药). It was Mr. Nobel's idea to create the prizes. During his life, Mr. Nobel made a lot of money from his invention. He put his money in a bank, and the money earned more money through interest (利息) from the bank. The money grew to be a very large amount.

Mr. Nobel decided to use his money to help scientists, artists, and people who worked to help others around the world. He created the Nobel Prizes to do this.

 The prizes set up by Mr. Nobel include physics, medicine, chemistry, literature, and peace. These five Nobel Prizes were first given out in 1901. Later, the Central Bank of Sweden (瑞典) made the Alfred Nobel Memorial Prize in Economic (经济) Science in 1968 to celebrate the bank's 300th year of business. All of the prizes are handed out in Stockholm (斯德哥尔摩) except the Peace Prize, which is presented in Oslo (奥斯陆).

Each person who receives a Nobel Prize is given a cash prize, a medal, and a certificate which explains the prize the person has won. The amount of money that each person receives is calculated from the interest earned from all of Mr. Nobel's money which is still in the bank. This interest is divided equally among the five prize winners in physics, medicine, chemistry, literature, and peace. The Central Bank of Sweden then pays an equal amount to the winner of the prize in economics.