University Microfilms, 1946-79. A large microfilm collection of periodicals from colonial times through the nineteenth century. An index identifies periodicals focused on particular topics. New York Times Index. A valuable source for finding newspaper coverage on a particular historical topic.
Topics tend to be grouped under broad subjects, with individual stories listed chronologically.
The index gives the date, section, page, and column of each story, which can then be found on microfilm. Even without reading the stories themselves, you can get detailed chronologies of events from this index. Official Index to the Times. Poole's Index to Periodical Literature, 1802-1881. Houghton Mifflin, 1892.