Here are a few links to great on-line art books. Some of these are out-of-print classics. I'll post more as I find them.
Many Classic On-Line Art Books on StudioProducts.com"The Painter In Oil" by Daniel Burleigh Parkhurst"Biography Of Sir Alma-Tadema" by Vern Grosvenor Swanson, Ph.D. "The Eclipse Of Classicism" by John William Godward"William Bouguereau", a biography by Damien Bartoli
"Blackboard Sketchings", by Frederick Whitney 1908
"The Essentials of Lettering", by Thomas E. French and Robert MeikleJohn 1909Online Art Books on the UPenn Archive"What is Art?" by Leo Tolstoy
"Mornings in Florence" by John Ruskin
"Seven Discourses On Art" by Sir Joshua Reynolds
"The American Drawing Book: a Manual For the Ameteur, and a Basis of Study For the Professional Artist" by J.G. Chapman, 1870"Memoirs of the Early Italian Painters" by Anna Jameson, 1890"The Notebooks Of Leonardo Da Vinci", by Jean Paul Richter, 1883"The Practice Of oil Painting And Of Drawing Associated With It", by Solomon J. Solomon, R.A. 1914Also, here is a list of some that you can cut and paste into your browser:
Frank Duveneck
Heermann, Norbert, 1918. Frank Duveneck
http://www.archive.org/details/frankduveneck00heeruoft
http://www.the-athenaeum.org/art/by_artist.php?id=391 (55 images)
William Merritt Chase
Roof, Katharine Metcalf, 1917. The life and art of William Merritt Chase
http://www.archive.org/details/lifeartofwilliam00roofiala
http://www.the-athenaeum.org/art/by_artist.php?id=106 (293 images)
Winslow Homer
Cox, Kenyon, 1914. Winslow Homer
http://www.archive.org/details/winslowhomer00coxkuoft
http://www.the-athenaeum.org/art/by_artist.php?id=91 (458 images)
George Inness
Inness, George Jr,, 1917. Life, Art and Letters of George Inness.
http://www.archive.org/details/lifeartandletter005237mbp
http://www.the-athenaeum.org/art/by_artist.php?id=371 (181 images)
James McNeill Whistler (just the latest of many)
Hartmann, Sadakichi, 1910. The Whistler book; a monograph of the life and position in art of James McNeill Whistler
http://www.archive.org/details/whistlerbookmono00hartiala
Macfall, Haldane, [1906?] Whistler
http://www.archive.org/details/whistler00macfiala
http://www.the-athenaeum.org/art/by_artist.php?id=428 (180 works)
Furst, Herbert, 1920. Frank Brangwyn, R.A (woodcuts)
http://www.archive.org/details/frankbrangwynra00braniala
Sparrow, Walter Shaw, 1915. A book of bridges (illustr. Brangwyn)
http://www.archive.org/details/bookofbridgesspa00sparrich
Brooklyn Museum, 1921 - Historical paintings of the Slavic nations
http://www.archive.org/details/historicalpainti00muchiala
Loomis, Andrew, 1951. Successful Drawing.
http://acid.noobgrinder.com/Loomis/Andrew%20Loomis%20-%20Successful%20Drawing.rar (direct download link)
Storey, G. A. The Theory and Practice of Perspective.
http://www.gutenberg.org/files/20165/20165-h.zip (direct download link)
Watson, Ernest W., 1955. How To Use Creative Perspective.
http://www.archive.org/details/howtousecreative036957mbp (poor scans)
Longfellow, William Pitt Preble, 1901. Applied perspective, for architects and painters.
http://www.archive.org/details/appliedperspecti00longrich
Miller, Leslie William, 1887. The essentials of perspective, with illustrations drawn by the author.
http://www.archive.org/details/essentialsofpers00mill
Great collection of scholarly articles on the history of perspective (Kim Veltman)
http://www.mmi.unimaas.nl/people/Veltman/publications.htmPerspective