Edison is known as one of the greatest inventors of his time. He invented so much that it is difficult to say which of his achievements is the greatest. He was an experimenter and a practical man more than a theoretician. Edison did not have any education. He went to school only for three months. Then he left it because the teacher considered him a dull boy. His mother became his teacher. The boy loved books and his mother said that he had a wonderful memory. When he first visited a public library and saw a lot of shelves with books he decided that he would know everything in the world. He measured the shelf and decided to read a foot of books every week. In 1868 Edison built his first patented invention - an electromagnetic device. It is said that he planned to ask three thousand dollars for his invention, though he secretly decided he would sell it for two thousand if necessary. He was invited to a meeting of businessmen who were interested in buying his invention, but when he was asked to name the price he was very nervous and quite unable to speak. "It is no use asking us a big price", said one of the businessmen, "we have already decided how much we will pay. Forty thousand dollars is our limit". With this money Edison established a workshop and began his career as a professional inventor at the age of twenty one. All his inventions were the result of hard work. He sometimes made thousands of experiments. According to his words the idea that a genius works only by inspiration was absurd. "Genius is 2 per cent inspiration and 98 per cent perspiration", he often said.