ROOM TEMPERATURE <i> by Nicholson Baker Grove Weidenfeld: $16.95; 144 pp. </i>

Many look but few observe, as Sherlock Holmes noted to Dr. Watson, and a technical writer named Mike, the narrator of this short second novel by Nicholson Baker (the first was “Mezzanine”), is definitely one of the observers. Bottle-feeding his six-month-old daughter, nicknamed “the Bug,” on a fall afternoon in Quincy, Mass., in the apartment he shares with his working wife, Patty, he asserts that “with a little concentration one’s whole life could be reconstructed from any single 20-minute period randomly or almost randomly selected.” He then proceeds to prove it.

Without leaving his rocking chair, Mike shuttles back and forth between his past as a precocious kid and college-dorm Romeo and his present as an awed new parent. His mode of travel is the long, intricate sentence, which he views as indispensable for the “careful interpretation and weighing” of “novelties of social and technological life.” His fuel consists of details so fine, and so finely observed (whether of nose-picking or model airplanes, the taste of Bic pens or the mutual sounding-out talk of newlyweds, the clucking noises the Bug makes or the shape of a spoonful of peanut butter, which leads him to imagine impishly what his wife, when pregnant, would have looked like in a wind tunnel), that they give off propulsive heat and spurt the reader along with delicious little jolts of recognition.

True, Mike’s life is a sheltered one, and Baker is blatantly showing off (like a teen-ager solving quadratic equations while winning a bubble-gum-blowing contest). “Room Temperature” has a smug, tour de force- y quality to it. But it also includes some of the most tender, most delicate interaction between husband and wife, adult and infant, in modern fiction, demonstrating what John Updike, no mean observer himself, meant when he wrote of artists who imitate God: “Details are the giant’s fingers. He seizes the stick and strips the bark and shows, burning beneath, the moist white wood of joy.”