Henry, Reginald Buchanan, M.D.
Reginald Buchanan Henry (1881-1969) was a physician and genealogist. In his book, Genealogies of the Families of the Presidents
, he used a numbering scheme
where the number assigned to a person indicates that person's position in the descendancy. Dr. Henry’s book is the earliest genealogy book published which employed this particular method and so it has come to be known as the Henry system