An antiquarian, historian and genealogist, Watson was fascinated by the survivals of the past, and people's memories of past events. His three-volume work, The Annals of Philadelphia
is an icon, called familiarly "Watson's Annals" and recognized immediately by contemporary scholars. It is filled with facts, opinions, gossip, descriptions of people and places, and past events.
The methods he employed to gather information included the collecting of oral histories, the use of questionnaires, and the acquisition of such physical survivals as fabric swatches and clippings from early newspapers.
A collection of Watson family papers is in the Joseph Downs Collection of the library at the Winterthur Museum; information is available by visiting Winterthur's website.