Bonds With the Past : Correspondence of four sisters brings an era back to life : ARISTOCRATS: Caroline, Emily, Louisa, and Sarah Lennox, 1740-1832, <i> By Stella Tillyard (Farrar, Straus & Giroux: $30; 406 pp.)</i>

Before I left England for the United States, I lived in Holland Park, an area of west London named for a Jacobean mansion, Holland House, which was partially destroyed by a bomb in World War II. Its grounds became a public park where I took walks on Sundays.

Reading Stella Tillyard’s “Aristocrats” about four 18th-Century sisters--Caroline, Emily, Louisa and Sarah Lennox--I discovered that Holland House was also once home to Caroline and her husband, Henry Fox. The tiny connection delighted me. Perhaps the peacocks I saw preening on the park’s woodland pathways were descendants of the birds introduced by Caroline. And surely the Lennox sisters must have strolled beneath the same south-facing portico where I had often lingered.

This kind of close bonding with the past also lies at the heart of Tillyard’s remarkable historical biography. Largely based on the correspondence of the four Lennox sisters, the book is enlivened by Tillyard’s own imaginative, almost novelistic marshaling of a million intimate details. She knows that wars and politics impose order on the jumble of past events, but it is the seemingly more trivial and material reminders--old buildings, clothes, kitchen implements, water closets and gossipy letters--that make the past seem real.

“We need the extraordinary, but we need the ordinary, too,” Tillyard says. It is her greatest achievement that she manages to describe both.

Thus we hear Sarah describing a failed effort to go on a diet, and all the sisters at times bemoaning the inconvenience and pain of “the French Lady’s visit” (their periods). Caroline recommends to Emily the new practice of inoculation--more risky then than now--for her babies. And there are innumerable discussions about decorating, private theatricals, family crises, illnesses and achievements, and visits to the spa of Bath.

Yet also woven into the fabric of the sisters’ story are all the sweeping social, political and philosophical changes of the day. Caroline and Emily avidly read Voltaire and Rousseau, and took from these great French philosophers their ideas on how to live. The sisters also experienced in a personal way the great democratizing events of the era, the Irish rebellion, the French Revolution and the American War of Independence.

Because of their direct descent from Louise de Keroualle, the favorite French mistress of Charles II, the sisters were Francophiles, and as outsiders they tended to favor various forms of emancipation. Caroline’s son, Charles James Fox, became a radical politician who brought about the British abolition of the slave trade in 1807. Emily’s son, Lord Edward Fitzgerald, was an Irish revolutionary who died in jail after capture by British troops.

In some ways, this was business as usual, Tillyard says: “The circumstance of male lives and opinions shaping female ones.” Yet she also shows that, despite many restrictions, the sisters were able to lead busy, fulfilling lives and that the degree of their fulfillment depended to some extent on their personalities and their ability to bend convention to their advantage.

Caroline and Emily, the cleverest sisters, both made marriages that suited them and allowed their talents to bloom.

Defying her parents, Caroline eloped with the charming, politically ambitious Henry Fox. Their marriage was always an equal partnership, domestically as well as intellectually. Politicians visiting Holland House were astonished to find that the Fox children, far from being tucked away in some distant country house like most aristocratic progeny, were not only present but indulged to an extreme degree.

Emily married a rich Irishman, James Fitzgerald, the Earl of Kildare. She was pretty, quick-witted, manipulative but charming. Though she hated being eternally pregnant, she adored her 22 children, and mourned the 12 who died of childhood illness. Based on her reading of Rousseau, Emily devised her own educational system--for her girls as well as her boys--that included vigorous outdoor pursuits such as swimming, gardening and hay-making, along with more traditional academic subjects.

Emily also caught the age’s new obsession with “sensibility”--a kind of emotionalism that included romantic love, very different from the old, aristocratic laissez faire attitude toward one’s spouse’s lovers. She fell in love with her children’s low-born tutor, William Ogilvie. What was more unusual was that she married Ogilvie, after her husband’s death, managing “the transition from adulteress to wife with magnificent aplomb.”

Sarah also tried to find her own way of life. Less sophisticated and less self-confident than Caroline or Emily, she stumbled more. Expecting to marry George III, who had a terrible crush on her, she was humiliated by the sudden announcement of his arranged marriage to a German princess, Charlotte of Mecklenberg. Later, Sarah fled a loveless first marriage via a short-lived, scandalous affair, spent years eating humble-pie for her relatives, and then fell in love with and married a military man, George Napier. His love helped boost Sarah’s flagging self-esteem, so that, years later, she was able to wangle a much-needed 800 a year pension out of the king on the basis of his earlier attachment to her.

Louisa, the most conventional of the sisters, married Thomas Conolly, the richest man in Ireland, and found her vocation managing Castletown, his huge estate, with its “46 servants, more than 90 hearths, four three-wheeled carriages, and constant improvements.” The house regularly fed 82 people daily. In a letter to Emily, Louisa noted, “I am very proud of having made 50 cheeses this summer.”

Sometimes akin to Jane Austen, sometimes as melodramatic as a Regency romance, “Aristocrats” may seem far distant from modern life. Yet there are moments when we can positively hear the shifting of historical gears--in Tillyard’s descriptions of London’s pleasure gardens where rich and poor could mingle freely, in Sarah’s middle-aged obsession with the military and Louisa’s philanthropic school building, both heralding the Victorian era, in Emily’s very modern love affair and many other small incidents, all of them nudging their age ever closer to ours.