The book will be of interest to everyone who is not indifferent to the opinions of great scientists about the value of Knowledge, about the ways of its expansion and the qualities necessary for the pioneers of science. But first of all, it is addressed to high schools to teach the art of thinking using specific examples. These examples are adapted fragments from the works, letters, diary entries, journalistic articles of classical scientists and scientists of our time, selected thematically. Attached are a Dictionary and an illustrated Index of names, with brief information about the characteristic activities and personalities of all the scientists mentioned.