FOR A WHILE, Phyllis Theroux thought she wanted to become a nun. Or, more accurately, she thought she ought to want to become a nun. As luck would have it however, the nuns did not want her and she went on to other things--things like marriage and raising children and gardening and, luckily for us, writing.

In her first book, California and Other States of Grace, Theroux detailed her childhood--the sweet mystery and lunacy of growing up in California at a certain time, and among a family of strong characters. This was a fine full blossom of a memoir that left the reader hoping for more.

Now, in Peripheral Visions, Theroux continues the story of her life in a certain chopped-up fashion. This book is a collection of essays which have appeared in various newspapers and magazines. They are essays which find Theroux on the East Coast--specifically in Washington, D.C.--more than in California and they are essays which pick up the threads of her life: husband now gone, children grown older, garden given way to weeds. And, finally, it is here, in the book's first essay, that Phyllis Theroux becomes a nun after all.

In a rented costume--"The black floor-length gown was obviously a graduation robe, the belt resembled a drapery cord. But the white cotton helmet covering my hair was authentic enough, the starched bib plausible and the veil was a separate rectangle of cloth the exact weight and weave it should be"--Theroux superficially enters the sisterhood. She spends one day, disguised, walking city streets, entering stores, dealing with sales clerks, waitresses, a surly garage mechanic. Some of Theroux's friends have tried to dissuade her from carrying out this experiment. "Suppose you meet a real nun?" one asks. "What would you say?" And in some ways it is a kind of dizzy-dame scheme, an episode from "I Love Lucy." In her first few minutes as a nun, Theroux's veil is lifted by the wind and sent sailing like some spooky bird to fetch up at the feet of two elderly ladies. And later in the day, without her glasses, Theroux wanders nearsightedly into broom closets in her search for a ladies' room. She cannot ask for assistance because "it is popularly believed that nuns don't go to the bathroom."

But Theroux is not looking for slapstick material here. She is not going through this for the laughs. There is something she needs to know about this disguise, something about being on the other side of that veil, looking out. She finds that sales clerks are chattier, waitresses more respectful and certain garage mechanics as surly as ever. But most of all she confirms what she has perhaps suspected all along: "I had been enough places and seen enough people to realize that for all the smiles and 'Sisters' and held-open doors, I had been in the world as a foreigner. . . . Kindness was oddly inhospitable at the roots. The world didn't allow a nun to understand; it didn't want sympathy, it wanted a blessing, a snatch of additional Truth."

Theroux has the ability to give us all snippets of additional Truth. In each of the 26 essays in this book, there are pure bright moments--especially in the conversations with her children and with her gardening colleague, Mr. Olson. Theroux writes about playboys and bullies and Bishop Fulton Sheen. She gives us deft sketches of a neighborhood wedding and a young babysitter about to lose her bearings in love. She offers further glimpses of her parents, those quirky Californians we met in her first book. She sets forth funny, throwaway lines on love, marriage and the human condition.

With all of this going for it, it doesn't seem quite fair to find fault, but an essay collection is something like a handful of shiny, near-perfect pearls. When you string them together, they don't always make quite the necklace you had in mind. There are small flaws that only begin to show up when set down side by side. Theroux has problems with words like "instinctually" and "hopefully." In one essay she pokes fun at Gloria Vanderbilt for publicly decrying the widespread misuse of "hopefully," but Theroux's barbs don't have much zing since she has already stumbled over that same word in her introduction to this book. Mistakes like this are all the more irritating because they might well have been caught in the editing process.

The larger problem with this book is one that is probably built into the essay form itself. Newspaper essays are always fleeting things. Today's insights wrap tomorrow's fishbones. Writers like Theroux have to package their work to meet certain limitations of time and space. As a result, when strung together, the limitations may show up as readily as the insights--unless special care is taken in the selection and arrangement of the pieces. In this book, Theroux's writing takes on a kind of gloss, a glibness that was never conspicuous when these pieces appeared originally--and singly. And it was certainly not apparent in her California memoir where she was released from the strictures of the essay form altogether.

Still, long or short, Phyllis Theroux can write. This book never calls that into question. Instead the question might be whether this is the best format for her talent. At the end of Peripheral Visions we have the feeling that the real Phyllis Theroux has eluded us. She has remained safe in her disguise all along. And when we look, all we are able to see is habit.