Nice. Good to see actual hard science books popularized and available for free.
The textbook industry is a criminal cartel shafting both the students/knowledge seekers and authors/professors. Hence i really appreciate the way you have made the pdf available both for free and for a nominal price; so thank you.
We need more hard science (Physics/Chemistry/Biology/etc.) content (books/articles/videos/etc.) on HN. For example, the interdisciplinary field of "Materials Science" (https://en.wikipedia.org/wiki/Materials_science) is one the most practical and important for our modern world and yet there is hardly any discussions/popularization about it.
I used to think that way about the publishing industry too, but I now think that this description is not deserved. Just observing it from an operational perspective: a laptop to type, software to edit, book printers that will talk to you, payment rails, and even access to world-class distribution: it’s all available to us now. On the other side of the market, students and teachers are not locked in either. Barriers to entry are nonexistent. For context, see the links I posted in my other comments on this page. It’s all in our hands!