Periodical articles on religion are like the plague of frogs in Egypt not only in number but in the fact that they appear in the most unlikely, not to say unsuitable, places. A special apparatus is indispensable to all who have any reason to try to keep track of them. Mr. Ernest Richardson, formerly librarian of Hartford Theological Seminary, now of Princeton University, an experienced hand, with the co-operation of several other bibliographers, has undertaken the laborious task of preparing a special index to this literature on the general plan of Poole's Index. The volume before us includes articles on religion published in the ten years, 1890 to 1899 inclusive, in not far from fifteen hundred periodicals. At a rough estimate, making no subtraction for repetition, the whole number of entries is between 60,000 and 70,000.