God bless that wonderful librarian in New York City who helped David McCullough with his early research

When David McCullough was in the very early stages of doing research for what would become his first book, the superb story of the Johnstown Flood, a very helpful librarian at the New York Public Library — God bless all librarians — suggested McCullough consult the DAB. Swallowing his pride, the inexperienced researcher said to the librarian, “What is the DAB?” The librarian showed McCullough where to find the multi-volume Dictionary of American Biography. The more than twenty books were on the shelf beside where McCullough had been sitting. From that point, McCullough’s research intensified. The rest is history.

Here is the brief Wikipedia article about the DAB: 

The Dictionary of American Biography (DAB) was a multi-volume dictionary published in New York City by Charles Scribner's Sonsunder the auspices of the American Council of Learned Societies (ACLS).

Read more via this link.