This is a Dover reprint of one of the earlier books in the MAA's Carus Mathematical Monographs (volume 6, first published in 1941). Two reviews are available through JSTOR: one from National Mathematics Magazine (the ancestor of Mathematics Magazine) and another from the American Mathematical Monthly. The first of these reviews starts by saying that "This Monograph measures up fully to the expectation of the reader who is acquainted (and who is not?) with the lucid and elegant presentation — oral and written — of Dunham Jackson." Modern readers may well not be acquainted with Jackson's expository prowess, but the book offers pretty good evidence for it. The author of that review concludes that the book "will render much service as a stimulating source of information on a very important branch of analysis." And so it has, over the last 60-some years.
Fernando Q. Gouvêa is grateful to Colby College for providing him with JSTOR access.