Every life is an experiment. A series of experiments, really. We test our theories about ourselves and the world through our actions, observing our own trials and shaping the hypotheses that reveal us — if only we can bear to look.

Author Andrea Barrett appreciates this cycle. It lies in the roots of her fiction, which reflects a fascination with mapping and understanding the natural world. But Barrett, a recipient of MacArthur and Guggenheim fellowships, also exhibits a shrewd understanding of the fragility and resilience of the human heart and how that intersects with our bold dreams of discovery, scientific or otherwise. We seek to explore what exists outside the boundaries of our knowledge but all too often remain strangers to the truth about ourselves.

This contradiction fuels her fiction, and in her first collection in nine years, Barrett revisits her themes with a scientist's precision and a poet's grace. "Natural History" revisits characters glimpsed in the previous story collections "Archangel," "Servants of the Map" and "Ship Fever," which won the National Book Award for fiction in 1996. These characters burn with a passion for knowledge, but that is not all they desire.

Still, you don't have to be familiar with Barrett's other works to appreciate these stories. At their center is Henrietta Atkins, a 19th-century teacher in rural New York. Henrietta observes her family and friends no less rigorously than she reviews the life cycles of insects and plants.

As part of her training, Henrietta's instructor advises: "Reduce every subject to its elements and study one difficulty at a time. Proceed step by step." But even this wise guidance can't explain the messiness of life.

In "Wonders of the Shore," her writer friend Daphne invites her to Celia Thaxter's island home for three weeks. A real-life poet, Thaxter proves a demanding host, and while Daphne placates and performs at Thaxter's salon, Henrietta's attention turns to a different sort of entanglement.

Questioning is Henrietta's natural state. She's a child in "The Regimental History," helping neighbors with their young child but more interested in the family's two grown brothers and their mysterious adventures in the Civil War.

In "Henrietta and Her Moths," she sets up specimens in her father's old workshop for her students, watching the creatures pupate more calmly than she notes her once-lively sister endure exhausting (and seemingly endless) pregnancies. Insects, it seems, are not so inscrutable as people.

Two stories shift from Henrietta's point of view. "The Accident" is mostly narrated by her niece Caroline, a barnstormer who experiences a shocking brush with death. In "Open House," one of Henrietta's best students finds himself torn between a life in science and staying close to home, not realizing his parents will decide for him.

The title novella links past and present. A descendant of Henrietta's navigates a shaky course through the scientific community she has abandoned. Henrietta's steady spirit, glimpsed in the work she left behind, draws her back. Step by step, she'll proceed.

Connie Ogle is a writer in Florida.

Natural History

By: Andrea Barrett.

Publisher: Norton, 224 pages, $26.95.