Synthesized answer
The provided passages do not contain enough information to answer the question about what evidence the author provides. The passages only state the title and page count of a book, "Early and Miscellaneous Letters by Johann Wolfgang von Goethe" [Passage 1]. There is no content from the letters themselves that would indicate what evidence the author presents.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: Early and Miscellaneous Letters by Johann Wolfgang von Goethe Pages: 440