Correlation 1. purpose of the chapter A complete history of correlation theory can scarcely be brought within the scope of this present study. It is indeed doubtful if an adequate history of that subject can be written by anyone now living except Professor Pearson. The published memoirs on correlation probably tell only part of the story, and need to be supplemented by his own recollections and unpublished notes and papers.The purpose of the present treatment is to present a somewhat abbreviated and schematic account of the development of the theory of correlation and its applications, and to furnish references to sources from which more details may be obtained. It is hoped that this may set the topic in historical perspective for those who-not having access to a large library-find it impossible to refer to the original papers; and that it may assist those who wish to go to the sources in finding important articles with greater ease than would be otherwise possible.Since correlation theory developed historically from the theory of probability, it has seemed necessary to make a brief reference to the mathematical equation for the probability surface of normal correlation. The nonmathematical reader who finds the next few paragraphs irksome, will find material more to his liking in Section 3.