Catholic Encyclopedia: Adelard of Bath: Short article on this 12th-century thinker by William Turner.
MacTutor History of Mathematics: Adelard of Bath: Biographical article with bibliography and links to related topics.
Medieval Sourcebook: Adelard of Bath: Excerpts from this thinker's Natural Questions, in which he argues that divine agency should not be invoked for those things which can be understood through reason.
Wikipedia: Adelard of Bath: Concise article with links.