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1、Unitl GREAT SCIENTISTS#JOHN SNOW DEFEATS “KING CHOLERA,#John Snow was a famous doctor in London so expert, indeed, that he attended Queen Victoria as her personal physician. But he became inspired when he thought about helping ordinary people exposed to cholera. This was the deadly disease of its da

2、y. Neither its cause nor its cure was understood. So many thousands of terrified people died every time there was an outbreak. John Snow wanted to face the challenge and solve this problem. He knew that cholera would never be controlled until its cause was found.#He became interested in two theories

3、 that possibly explained how cholera killed people. The first suggested that cholera multiplied in the air, a cloud of dangerous gas floated around until it found its victims. From the stomach the disease quickly attacked the body and soon the affected person died.#John Snow suspected that the secon

4、d theory was correct but he needed evidence. So when another outbreak hit London in 1854, he was ready to begin his enquiry. As the disease spread quickly through poor neighbourhoods, he began to gather information. In two particular streets, the cholera outbreak was so severe that more than 500 peo

5、ple died in ten days. He was determined to find out why.#First he marked on a map the exact places where all the dead people have lived. This gave him a valuable clue about the cause of the disease. Many of the deaths were near the water pump in Broad Street （especially numbers 163738 and 40）. He al

6、so noticed that some houses （such as 20 and 21 Broad Street and 8 and 9 Cambridge Street） had had no deaths. He had not foreseen this, so he made further investigations. He discovered that these people worked in the pub at 7 Cambridge Street. They had been given free beer and so had not drunk the wa

7、ter from the pump. It seemed that the water was to blame.#Next, John Snow looked into the source of the water for these two streets. He found that it came from the river polluted by the dirty water from London. He immediately told the astonished people in Broad Street to remove the handle from the p

8、ump so that it could not be used. Soon aftenvards the disease slowed down. He had shown that cholera was spread by genns and not in a cloud of gas.#In another part of London, he found supporting evidence from two other deaths that were linked to the Broad Street outbreak. A woman, who had moved away

9、 from Broad Street, liked the water from the pump so much that she had it delivered to her house every day. Both she and her daughter died of cholera after drinking the water. With this extra evidence John Snow was able to announce with certainty that polluted water carried the virus.#To prevent thi

10、s from happening again, John Snow suggested that the source of all the water supplies be examined. The water companies were instructed not to expose people to polluted water any more. Finally #King Cholera, was defeated.#COPERNICUS, REVOLUTIONAY THEORY#Nicolaus Copernicus was frightened and his mind

11、 was confused. Although he had tried to ignore them, all his mathematical calculations led to the same conclusion:# that the earth was not the centre of the solar system. Only if you put the sun there did the movements of the other planets in the sky make sense. Yet he could not tell anyone about hi

12、s theory as the powerful Christian Church would have punished him for even suggesting such an idea. They believed God had made the world and for that reason the earth was special and must be the centre of the solar system.#The problem arose because astronomers had noticed that some planets in the sk

13、y seemed to stop, move backward and then go forward in a loop. Others appeared brighter at times and less bright at others. This was very strange if the earth was the centre of the solar system and all planets went around it.#Copernicus had thought long and hard about these problems and tried to fin

14、d an answer. He had collected observations of the stars and used all his mathematical knowledge to explain them. But only new theory could do that. So behveen 1510 and 1514 he worked on it, gradually improving his theory until he felt it was complete.#In 1514 he showed it privately to his friends. T

15、he changes he made to the old theory were revolutionary. He placed a fixed sun at the centre of the solar system with the planets going round it and only the moon still going around the earth. He also suggested that the earth was spinning as it went around the sun and this explained changes in the m

16、ovement of the planets and in the brightness of the stars. His friends were enthusiastic and encouraged him to publish his ideas, but Copernicus was cautious. He did not want to be attacked by the Christian Church, so he only published it as he lay dying in 1543.#Certainly he was right to be careful. The Christian Church rejected his theory, saying it was against God#s idea and people who supported it would be attacked. Yet Copernicus# theory is now the basis on which all our id