While googling for information on the Virial Theorem, I ran across a really cool page hosted at the Harvard ADS system. ADS stands for Astrophysics Data System, and it is primarily an abstract search engine that helps you locate journal articles mostly in the realm of Astronomy and Astrophysics, but they also have a small virtual library of books that you can freely download.
Here are the titles I found interesting:
- The Foundations of Celestial Mechanics by George W. Collins, II
- The Fundamentals of Stellar Astrophysics, by George W. Collins, II
- Fundamental Numerical Methods and Data Analysis by George W. Collins, II
- The Virial Theorem in Stellar Astrophysics, by George W. Collins, II
(1978, Pachart Publishing House, Tuscon, Arizona).
If you want to concatenate all the separate PDF chapters, I recommend using the texexec method oulined in this web page by Matthew Skala.