Answered By: Joe Bourneuf Last Updated: Apr 24, 2017 Views: 23
The history of the development of the classification system (now referred to as "Old Widener", although it was originally developed for use in Gore Hall, Widener's predecessor) is described in this pamphlet, which fortunately is available digitally from this Hathitrust link:
An index guide to the shelf classification of the Harvard college library ...
[Cambridge, Mass.] Printed for the library, 1905. 43 p. ( Its Special publications. v. 4 )
Contents: I. Plans of the bookstacks.--II. Index of shelf-marks.--III. Index of subjects.
Widener | B 7849.05 [WorldCat/OCLC: 18328389]
Credit for the implementation, and probably much of the detailed development of this system, should go to Justin Windsor, Librarian of Harvard College 1877-1897, and his successor 1898-1910, and author of this historical sketch, William Coolidge Lane.