I have to agree with this. My physics education was sort of being dumped into late 20th century physics and could not understood how we got to quantum and relativity. It wasn't until recently that I went back and kind of walked through the history of physics from the natural philosophy days to the cavendish in the late 1800s that modern physics started to make sense.
Generally speaking, I find that the more expensive a rare academic tome is, the more likely there are legal/etc. versions online (PDFs, HTML, DjVu, etc.), indexed by Google. That seems to be much more true for STEM texts than those of the humanities, though.
