Continuum Mechanics books, Abramowitz and Stegun, downloadable
Books on continuum mechanics freely available on the web. Of particular note,
"Introduction to Continuum Mechanics for Engineers" by Ray M. Bowen
"Continuum Mechanics" by George Backus
"Continuum Mechanics" by Brian Kennett
both at http://samizdat.mines.edu
The samizdat site has links to many other texts, particularly in geophysical applications.
Not continuum mechanics but useful if you have ever used the hard copy:
"Abramowitz and Stegun: Handbook of Mathematical Functions"
The copyright is in the public domain. The book can be downloaded from http://www.math.sfu.ca/~cbm/aands
Keep the html version on your PC and you can get that Bessel function relation in no time.