Can I find classical works on Physics online somewhere?
I would love to know the answer to this question too. There is probably not much available for free. You might try the Gutenberg project
A search for "physics" returns some things by Einstein and something by Poincare.
Often, you have to be ready at just the right time. Both APS/AIP (for the Physical Review Journals) and the Royal Society had short periods where they made all their "classics" publicly available. These were during some big n-centennial kind of celebration. Window gone - opportunity lost.
Separate names with a comma.