The book has no illustrations or index. It may have numerous typos or missing text. However, purchasers can download a free scanned copy of the original rare book from the publisher's website (GeneralBooksClub.com). You can also preview excerpts of the book there. Purchasers are also entitled to a free trial membership in the General Books Club where they can select from more than a million books without charge. Original Publisher: New York: Courant Institute of Mathematical Sciences, New York University; Publication date: 1954; Subjects: Functional analysis; Perturbation (Mathematics); Eigenvalues; Mathematics / General; Mathematics / Matrices; Mathematics / Differential Equations; Mathematics / Functional Analysis;