Project Gutenberg provides downloads of books which are in the public domain. Since the copywrite on books generally expires after 100 years, the Gutenberg collection has quite a few great scientific works.
As an extra service, the gutenberg website provides a daily list of their top 100 downloads. Here is a sampling of today's list.
- The Outline of Science, Vol. 1 (of 4) by J. Arthur Thomson (833)
- Manners, Customs, and Dress During the Middle Ages and During the Renaissance Period by P. L. Jacob (685)
- Illustrated History of Furniture by Frederick Litchfield (496)
- Searchlights on Health by B. G. Jefferis and J. L. Nichols (398)
- The Kama Sutra of Vatsyayana by Vatsyayana (354)
- History of the United States by Charles A. Beard and Mary Ritter Beard (337)
- Inaugural Presidential Address by Barack Obama (316)
- Our Day by William Ambrose Spicer (305)
- Pride and Prejudice by Jane Austen (293)
- The Atlas of Ancient and Classical Geography by Samuel Butler (285)
- The Beginner's American History by D. H. Montgomery (274)
- The Adventures of Huckleberry Finn by Mark Twain (270)
- The People's Common Sense Medical Adviser in Plain English by Ray Vaughn Pierce (261)
- Woman as Decoration by Emily Burbank (259)
- General Science by Bertha M. Clark (254)
- Nouvelles histoires extraordinaires by Edgar Allan Poe (254)
- Wuthering Heights by Emily Brontë (214)
- The Iliad by Homer (214)
- Myths and Legends of Ancient Greece and Rome by E.M. Berens (214)
- The Practice and Science of Drawing by Harold Speed (211)
- Sex by Henry Stanton (208)
- Elements of Structural and Systematic Botany by Douglas Houghton Campbell (207)
- The Mafulu by Robert Wood Williamson (199)
- Amusements in Mathematics by Henry Ernest Dudeney (195)
- The Notebooks of Leonardo Da Vinci — Complete by Leonardo da Vinci (195)
Wow, the Illustrated History of Furniture was number 3 yesterday, and it is kind of depressing it was more popular than the Notebooks of Leonard Da Vinci, but that is the modern age, and why not?
