BOOK REVIEW / NONFICTION : An Awakening of Intense Emotions : THE NAKED HEART <i> by Peter Gay</i> ; W.W. Norton $29.95, 420 pages

Reading Peter Gay on the 19th Century is like being shown around a city, say Paris or Berlin, by a charming guide who is enthusiastic, knowledgeable and slightly eccentric.

At every turn in the tour, he presents a new vista, a new juxtaposition of scenes, a fresh illumination of a view you had been acquainted with but had never seen quite this way.

Gay’s eccentricity is that he sees history, and writes it, as a confirmed disciple of Sigmund Freud. A Freudian interpretation of history is definitely not at the center of American historiography these days.

But in Gay’s capable hands, the Freudian lens turns out to be an engaging method of photographing a century that by now seems at once remote and hauntingly familiar.

This is the fourth book in a planned series of five on middle-class 19th-Century culture by Gay, a history professor emeritus at Yale. The series, called “The Bourgeois Experience: Victoria to Freud,” has previously covered sexuality, love and aggression.

“The Naked Heart” is about the emergence of the life of the self in 19th-Century thought and expression. People began to express their feelings more intensely, and with more interest, than they generally had before.

Gay’s setting is largely Europe, and in Europe he focuses on France, Germany and England, with bows to the United States, Russia, the Low Countries and so forth. Although he says he is writing about the feelings and activities of the educated middle classes, the bulk of the book is about what those classes listened to in concert halls, read in books, looked at in museums.

The people you meet in these pages are historians, writers, painters, poets, psychologists, and Gay’s subject is their rendering of the human heart as they saw it.

In the course of our tour we learn many curious things. Gay has, for example, a fascinating account of the elevation of instrumental music to a queen if not king of the arts. This was an attitude encouraged by the Romantic movement early in the century, and taken up especially by Germans, who saw in it, as they moved toward a unified state, a symbol of the German soul.

To the same end the Germans came to venerate Rembrandt, finding in his highly psychologicalself-portraits a foretelling of the “inwardness” they came to value so highly as a national characteristic. But not only the Germans.

“Rembrandt’s late self-portraits,” Gay writes, “. . . appeared to Victorian viewers, and not just Germans, as highly self-conscious psychological studies, the culmination of a lifelong quest for self-understanding.”

It is his theory that even as Europe leaped forward in industrial development and extended its empires around the world, its thinkers and artists were on their own, pre-Freudian quest for self-understanding.

Charles Dickens is an example. Gay writes that although Dickens was derided as being too sentimental to be psychologically acute, he actually deftly sketched people in the grip of various neuroses, from a young person in “Little Dorrit” who “infuriates his little world with obsessive schemes to appear selfless” to “the twisted mind of the killer.”

Of David Copperfield, Gay writes: “Half a century before Freud, Dickens knew that the most innocent can damn themselves as the most guilty.”

Gay finds Freud handy to explain some phenomena. Talking about the multiplication of private diaries, Gay observes:

“Like other humans, the Victorians employed defensive stratagems to drive unacceptable wishes into inaccessible hiding places; when they did reach the surface of awareness (and were duly recorded), they came disguised and distorted as inexplicable feelings or strange dreams, and were left uninterpreted. Diarists could not read the language of their unconscious.”

It helps in reading “The Naked Heart” to have a fair acquaintance with the characters who people it. The sections on Dickens, Henry James and Goethe, for instance, are the more legible if you know them. If you don’t know Chateaubriand and Fontane, as I alas don’t, you are left in wistful ignorance.

Yet just when you fear that your attention is about to wander, Gay, always the hopeful guide, shows you yet another curiosity. In the section on the great growth of letter-writing, he points out how much of it was due to the invention of the prepaid penny post. Introduced in Britain in 1840, it greatly cut the cost and increased the reliability of mailing letters. By 1855 all letters in the United States were prepaid and stamped with adhesive stamps.

“The Naked Heart” is a beguiling and instructive book.