Andrew Loomis

"As a student I thought there was a formula of some kind that I would get hold of somewhere, and thereby become an artist. There is a formula, but it has not been in books. It is really plain old courage, standing on one's own feet, and forever seeking enlightenment, courage to develop your way, but learning from the other fellow; experimentation with your own ideas, observing for yourself, a rigid discipline of doing over that which you can improve." -Andrew Loomis

Andrew Loomis' books are out of print, and any copies you may find will usually cost a hundred dollars or more. However, his books are freely available over the internet. I believe this goes against copyright law, but I have not heard of anyone being asked to remove copies that are available to download.