History of the Encyclopædia Britannica the criteria by which the articles were sorted were not obvious even to scholars, despite Dr. Adler's claims that the sorting followed naturally from the "Propædia's" outline of all knowledge. In 1985, the "Britannica" responded to reader requests by restoring the index as a two-volume set. The number of topics indexed by the "Britannica" has fluctuated from 500,000 (1985, the same as in 1954) to 400,000 (1989,1991) to 700,000 in the current 2007 print version. Presumably, this recent increase reflects the introduction of efficient electronic indexing, since the size of the encyclopedia has remained nearly constant at approximately 40 million
Collier's Encyclopedia about two-fifths of the pages. Bibliographies are found in the last volume which also contains the 450,000 entry essential index. An annual "Collier's Year Book" was also published. In 1998 Microsoft bought the rights to Collier's electronic version and incorporated it into its "Encarta" electronic encyclopedia. Atlas Editions (formerly Collier Newfield) retained the rights to publish the encyclopedia in book form, though since then, Collier's has ceased to be in print. A well-known comparison is that of Kenneth Kister, who gave a qualitative and quantitative comparison of "Collier's Encyclopedia" with the "Encyclopædia Britannica" and the "Encyclopedia Americana". For the "quantitative"