During that time, Franklin spent only 18 months back in Philadelphia. In London, Franklin had a platonic relationship with his landlady, the widow Margaret Stevenson. He was like a father to her daughter Polly. They rapidly became his London family & home-base with Mrs. Stevenson managing the daily household details for him.
In 1770 she married William Hewson, a brilliant young physician & anatomist, who 4 years later died from an infection incurred while dissecting a cadaver. Polly devoted the rest of her life to the care & education of her 2 sons & daughter.
From 1775, Franklin tried to persuade her to move to America, & in 1784–85 she & the children did visit him in the new nation. Finally in 1786, she brought her family to Philadelphia, & was at Franklin's bedside when he died (1790), 5 years before her own death at her son’s home near Bristol, Pa.
About 170 letters between the bright, spirited woman, & the fatherly philosopher survive. They are full of humor & good will, plus serious science to speculation on marriage & public affairs, & later reports on growing children & grandchildren.
In 1783 he wrote: “In looking forward,—Twenty-five Years seems a long Period; but in looking back, how short! Could you imagine that ’tis now full a Quarter of a Century since we were first acquainted! It was in 1757. During the greatest Part of the Time I lived in the same House with my dear deceased Friend your Mother; of course you & I saw & convers’d with each other much & often. It is to all our Honours, that in all that time we never had among us the smallest Misunderstanding. Our Friendship has been all clear Sunshine, without any the least Cloud in its Hemisphere.”
See:
“From Benjamin Franklin to Mary Stevenson, 9 January 1765,” Founders Online, National Archives
The Papers of Benjamin Franklin, vol. 12, January 1, through December 31, 1765, ed. Leonard W. Labaree. New Haven and London: Yale University Press, 1967, pp. 16–17
James M. Stifler, “My Dear Girl” The Correspondence of Benjamin Franklin with Polly Stevenson, Georgiana & Catherine Shipley (N.Y., 1927).
Whitfield J. Bell, Jr., “‘All Clear Sunshine’: New Letters of Franklin & Mary Stevenson Hewson,” APS Proc., c 1956, 521–36, which describes the extent & character of their correspondence.
"For You My Needle With Delight I Plied" In The Words of Women
Eight of Franklin's letters to her appear in his 1769 edition of Experiments & Observations on Electricity.