Immigration Waves in American HistoryImmigration means to move from one country to another which is a permanent move, so if you go to live and work in a country for several years, you dont immigrate to it. In a long time ago, immigration happened all over the world, most people who immigrate to American in order to improve their economic or social situation, so There are three waves of immigrants in American history. As we know, the first wave of immigrants happened in the seventeenth century, and most immigrants were from Western Europe. At that time, In British, people who want to have a better life were not prohibited from immigrating, so many people moved to America, therefore the first permanent settlement was the British. At the same time, the French, Spanish, and Dutch also immigrated to the US, but only a few of people moved to US, and about 20 percent of the population was African American. As with the rapid development of economy which immigration was controlled in the 1790s, the Naturalization Act of 1798 required immigrants to live in the US a certain years before they became citizens to limit densities of immigrants. Now lets look at the second wave of immigrant which happened between 1840 and 1920. During this wave, due to the industrial revolution, its brought a big change for immigrant, and about 80 percent of immigrants who about 37 million people were from all over Europe. Chinese workers contracted to work in American company before they left home. In the 1891, to control the immigrant, the INS only opened in the Ellis Island, however between 1892 and 1954, when Eillis Island was closed, about 12 million immigrants entered through there, most from Europe. Then, the US government limited to immigrant with laws which passed a quota system.Finally, the third wave in the period from 1965 to the present time, in 1965, with the quota system was abolished so that during 1970s and 1980s, about 80 percent of the immigrants were from Latin America and Asia. Each year, after 1965, many people wanted to immigrate to the US.This led to the Immigration Act of 1990, which raised the yearly limit from 290,000 to 700,000.However, from 1990 to the present, the actual number has closer to 1 million, it is precisely because many people realize that the countrys greatest strength is the diversity of its people. So, the old melting pot ideal has been replaced with the ideal of cultural diversity, with recognizing the importance of Americans many different cultural backgrounds.Generally speaking, there were three waves of immigration to US, people are to find a better work and life which to move to the US.在多年收治肝病、出血热、麻疹、艾滋病等传染病的临床实践中，逐步认识到中医药在传染病防治领域的优势，因此在制定医院长期发展规划中，有步骤的增加中医药在整体医疗工作中的比重，不断加强中医学科建设several group number, then with b a, =c,c is is methyl b two vertical box between of accurate size. Per-23 measurement, such as proceeds of c values are equal and equal to the design value, then the vertical installation accurate. For example a, b, and c valueswhile on horizontal vertical errors for measurement, General in iron angle code bit at measurement level points grid errors, specific method is from baseline to methyl vertical box center line distance for a, to b vertical box distance for b, list can measured