and earlier this week I spent a whole day downloading free PDF scans of old math books
Did you know you can get both volumes of Chrystal's Algebra that way? Plus Neugebauer's Mathematical Cuneiform Texts! And Whitehead's Axioms of Projective Geometry!
I also learned there are places that will print and bind some google books for you for only about $5 each, with maybe another $5 for shipping if in-store pick-up isn't convenient. So I can get a copy of Ernst Bloch's Thomas Münzer als Theologe der Revolution for about $10
And you could waste your time doing that, too!
Navigating the air: a scientific statement of the progress ...Aero Club of America 1907
http://books.google.com/books?id=a_aKWhvdtrQC&printsec=frontcover&dq=Aero+Club+of+America&hl=en&ei=kno-TuzmAYSGsAKPnoE_&sa=X&oi=book_result&ct=result&resnum=4&ved=0CDoQ6AEwAw#v=onepage&q&f=falsehttp://www.google.com/search?tbo=p&tbm=bks&q=aeronautics&tbs=,bkv:e&num=10#q=aeronautics&hl=en&tbs=bkv:r&tbm=bks&source=lnt&sa=X&ei=j3s-Tpf-JvDMsQKUs4Qc&ved=0CBAQpwUoAw&bav=on.2,or.r_gc.r_pw.&fp=64d09540ea05943f&biw=1147&bih=844