Alexander Bain, Moral Science: A Compendium of Ethics Bain's 1869 work on ethics presented by the University of Michigan Library as part of the Making of America digital library of primary sources.
Gordon Graham, "Scottish Philosophy in the 19th Century" in Stanford Encyclopedia of Philosophy. An excellent summary of Bain's psychology and how it differs from Reid, Ferrier, and Hamilton, where Bain is viewed as a founder of empirical psychology.
Robert M. Young, "Alexander Bain: Transition from Introspective Psychology to Experimental Psychophysiology" in Mind, Brain and Adaptation in the Nineteenth Century. An online chapter on Bain's psychology from a well-received book on the mind-body problem.