Where did the author use Ethos in this part of the book to convince the reader?

The author, Napoleon Hill, uses Ethos in this part of the book "Think and Grow Rich" by leveraging his credibility and authority as a successful self-help author. He uses the concept of the 'Master Mind' to convince the reader about the power of collective thinking and collaboration. This is a form of Ethos as he is appealing to the reader's sense of trust in his expertise and experience. He is essentially saying, "Trust me, I know this because I have studied it and seen it work." This is a classic use of Ethos to persuade the reader to accept his argument.