ONE of the pleasures of a good biography is that it brings into focus the achievements of its subject but also brings him or her down to eye level, so to speak, letting the reader get to know a real human being who walked on the ground.There is, after all, something comfortably universal about the rhythm of a life story; even geniuses were schoolchildren once, and wrote letters home, and considered where to go to school and where to get a job. And so this approach to biography does not denigrate but rather enhances the subject's accomplishments. "The Jameses: A Family Narrative," by R.W.B. Lewis, is just this sort of biography. He has woven a rich tapestry of many lives, but principally those of William James, the psychologist and philosopher; his younger brother Henry James, the novelist; their sister, Alice, and their parents and younger brothers. We appreciate the achievements of two world-class geniuses, and one might-have-been (Alice, but for her health problems and "nervousness"). And we see the Jameses as human beings - as very human bein gs - in tender mutual support but also lively intellectual and other rivalry. The immigrant ancestor of the James family in America was William James of Albany, N.Y., who came over from County Cavan, Ireland, in 1789 as a young man of 18. The Jameses of County Cavan were Presbyterians and thus denied ownership of their land by the ruling Anglo-Irish. Caught between the Anglo-Irish, whom they outnumbered two to one but did not outrank, and far more numerous Roman Catholics, many Irish Protestants saw their best hope for the future in coming to America. William James certainly succeeded in the new nation. Settling in Albany, he built up a fortune that was second in the country only to that of John Jacob Astor and that included ownership of all of Syracuse, N.Y., then a somewhat swampy village. William tried to cut out of his will two of his sons, including Henry (later known as Henry James Senior after his son, Henry, had come into his own as a writer). But the will was successfully contested and Henry received a legacy that left him, as he is said to have murmured when he heard about it, "Leisured for life." This was the estate that supported thousands and thousands of miles of travel, mostly European, by Henry Sr. and his family. This travel led to rather disrupted educations for the children and to also a sense that they were neither American nor European but simply "Jamesian." The Jameses had their collective dark side; the most notable manifestation of this was the trouble many of them had with depression and mental instability. Henry Sr. experienced in 1844 an episode of fundamental existential fear, a "vastation," as he called it. His son William went through something similar in Rome, with his brother Henry beside him cheerfully oblivious to William's distress. Henry went through a serious depression toward the end of his life, and Alice had such difficulties throughout her life. She and her youngest brother, Robertson, each spent some time in mental institutions. There was almost always sunshine, though, after the "moral thunderstorms." The Jameses are not exactly virgin territory for a biographer. The collective and multigenerational approach is part of what distinguishes this book. One of the stories the book tells in passing, so to speak, is that of how a 19th-century family managed to keep connected to its many children over miles and oceans and years. They had the advantages of affluence, let there be no doubt. That Henry and Alice never had families of their own probably helped keep the family of origin more closely knit. But it is still striking how a family not far removed from the time when crossing the ocean was a once-in-a-lifetime event, and usually a one-way trip, managed to keep so closely in touch, and not just physically but mentally.