Thomas Edison could never be happy only because someone said he was a genius. "There is no such thing as genius," Edison said, He said that what people called genius was mostly hard work. From his earliest days as a child he wondered about the secrets of nature. Nature, he often said, is full of secrets. He tried to understand them; then, he tried to learn what could usefully be done with them. Edison enjoyed thinking. He knew that most people will do almost anything instead of the difficult work of thinking, especially if they do not think very often. But he knew, too, that thinking can give men enjoyment and pleasure. Edison could not understand how anyone could be uninterested in life. As he loved to think, he also loved to work. On the day he became 75 years old, someone asked him what ideas he had about life. "Work, "he answered, "Discovering the secrets of nature and using them to make men happier.” He said he had enough inventions in his mind to give him another 100 years of work.