BOOK REVIEW : Investigating the Secret Life of France : A HISTORY OF PRIVATE LIFE, VOL. 5, Riddles of Identity in Modern Times, <i> Edited by Antoine Prost and Gerard Vincent</i> , translated by Arthur Goldhammer Harvard University Press, $39.95; 615 pages

“The history of private life,” declares Gerard Vincent, “is a history of various kinds of fear.”

And fear of fat, he suggests, may be as important in understanding our era as fear of nuclear apocalypse.

Vincent is one of nine historians who have contributed long and lavishly illustrated essays to the fifth and final volume of “The History of Private Life,” a French series that studies the intimacies of private life from the ancient world to the 20th Century.

In the valedictory title of the series, the specific points of inquiry range from the cult of the bathroom mirror to the orthodoxies of French communism and the inner life of French Jews--but the essential idea is private life as the subtext of history. And so, as Vincent discerns, the pursuit of physical perfection takes on the force of true belief, and the full-length bathroom mirror functions as a ritual object.

The new volume--and the series itself--are broadly preoccupied with the relationship between the impersonal forces of history and the very notion of privacy. Thus co-editor Antoine Prost, for example, suggests that our modern sense of privacy is shaped by something as fundamental as the number of rooms in the family home.

“In a very real sense the 20th Century has been characterized by the conquest of space, but not by astronauts,” he writes. “It is living space that has been conquered, as more and more people acquire the room without which a full-fledged private life is impossible.”

And once privacy is assured, as Prost discerns, the focus of daily life shifts from neighborhood and family, church and workplace, to the shrine of the bathroom. “The narcissistic satisfactions of the bath are freighted with dreams and memories,” he writes. “The body is prepared as if a gift were to be made of it.”

Several of the more commanding voices in the latest volume of the series are no longer speaking of history at all--they are deep into an existential meditation on the very meaning of life. Perhaps the best example is co-editor Vincent’s “A History of Secrets?” an intentionally outrageous essay that takes the premise of the book quite literally: Vincent studies the secret as the essence of privacy.

“Sharing secrets--whether among the membership of a club for gentlemen, Freemasons, terrorists, a religious sect, a young gang, or a homosexual coterie--is a way out of the hell of solitude,” he concludes. “The shared secret establishes a community that lives in invigorating fear of a leak. Secrets fascinate.”

The new volume is dense with facts--but not as daunting as one might suppose. The design of the series, including useful marginal headings and generous white space that almost invites note-taking, is superb.

And the text is leavened with an abundant display of imagery--works of art, documentary photographs, historical artifacts--which amount to an elaboration of the prose rather than mere decoration. As a result, all five volumes of the series are probably no more type-heavy than 2 1/2 copies of “Harlot’s Ghost.”

A tendency that was increasingly visible in earlier volumes of the series is full-blown here: Despite the occasional sidelong glance at other countries and other cultures, the work is almost exclusively concerned with the French experience of private life.

Perhaps as a corrective, the Harvard University Press edition of the new volume features three additional essays--including Elaine Tyler May’s “Myths and Realities of the American Family”--that attempt to push the work beyond the borders of France.

But the real appeal and utility of the book transcend its Gallic setting. In fact, the entire series amounts to a vast treasury of human thought and experience, a sourcebook of ideas and images. At times lyrical, then analytical, but always provocative, “A History of Private Life” is a tool for the analyst and the novelist as much as the historian and the anthropologist.

Next: Schuyler Ingle reviews “Afghanistan” by Alex Ullman (Ticknor & Fields).