Forebears of Sir Francis Ronalds' mother Jane née Field (1766-1852) had been merchants in the City of London since the 17th century but, by the mid-19th century, their descendants had sufficient education, money and status to follow other paths in life.
Of those whose goal was to rise above the merchant class, the most successful was Sir Francis' uncle George Field (Snr) and his offspring. They did this by marrying well, migrating to their in-laws' businesses and shaking off the shackles of the family's Unitarian religion.
George Field Snr (1771-1848) was apprenticed when he turned 14 and later ran a merchant business next door to Ronalds cheesemongers in Thames Street. It had an international footprint, with his brother being based in St Petersburg. George Snr married Ann, the daughter of John Bolland, a hop merchant and later MP. Sir William Bolland, Baron of the Court of the Exchequer, was both Ann's first cousin and her brother-in-law. Other sisters married John Lonsdale, the Bishop of Lichfield, and Colonial administrator General Sir William Reid.
George Snr and Ann's son George Jnr (1798-1875) wed Susan Hanbury, the daughter of a banker and merchant. He became a hop merchant and later a magistrate and High Sheriff in Kent. Burke's Landed Gentry (1875) listed the family as "Field of Ashurst Park" in reference to their "Seat" near Royal Tunbridge Wells, where they had eleven live-in servants. George Jnr amassed a famous art collection which, as he wrote to Sir Francis, "I flatter myself would please you to look at" and also enjoyed visiting Sir Francis at the Kew Observatory.
George Jnr and Susan's eldest son George Hanbury Field (c.1835-1901) was educated at Eton and Oxford. He played first-class cricket and was briefly a barrister before becoming a brewery owner, bank director and Deputy Lieutenant of Kent. He married twice. His first wife was Lady Georgiana Turnour, daughter of the Earl of Winterton, and his second the Hon Emily Hardinge, daughter of Viscount Hardinge. The family employed 13 servants in the house, including a valet and lady's maid. In addition there were three grooms in the stables, three live-in gardeners with their families, and the estate carpenter in "The Lodge" of Ashurst Park. Significant enhancements were made to the local church as a memorial to him.
This side of the family came to an end soon afterwards through lack of heirs.
George Hanbury Field's entry in Wikipedia
The letter quoted is held in the Ronalds Archive at the IET. Much of this information was researched by Elsie Day.