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
Encyclopædia Britannica main competitor was the general encyclopaedia of Ephraim Chambers and, soon thereafter, "Rees's Cyclopædia" and Coleridge's "Encyclopædia Metropolitana". In the 20th century, successful competitors included "Collier's Encyclopedia", the "Encyclopedia Americana", and the "World Book Encyclopedia". Nevertheless, from the 9th edition onwards, the "Britannica" was widely considered to have the greatest authority of any general English language encyclopaedia, especially because of its broad coverage and eminent authors. The print version of the "Britannica" was significantly more expensive than its competitors. Since the early 1990s, the "Britannica" has faced new challenges from digital information sources. The Internet, facilitated by the development of