There is a free version of the Feynman Lectures on Physics provided by Caltech.
See also http://www.feynmanlectures.info/
Caltech reminds that:
“However, we want to be clear that this edition is only free to read online, and this posting does not transfer any right to download all or any portion of The Feynman Lectures on Physics for any purpose.”
“This edition has been designed for ease of reading on devices of any size or shape; text, figures and equations can all be zoomed without degradation.”