In the days before kitchen clocks and automatic timers, cooking instructions never were measured in minutes. Sir Kenelm Digby, a 17th-century Englishman much given to passing along any culinary information he came upon (one of his recipes is headed, "My Lord d'Aubigny eats Red Herrings thus boyl'd"), explained to the readers of his "Two Treatises" that a certain dish must be left to thicken "until you see your shadow in it," or "till it begins to blink." As for brewing tea, the leaves should steep no longer "than whiles you can say the Miserere Psalm very leisurely."

The appearance of meat thermometers and timers that go bing in the night took some of the fun out of cookbooks but, supposedly, it replaced such charming, slapdash methods with the rigors of science. In 30 minutes (or when the thermometer registered an inner temperature of 180 degrees) the meat would be done and the confident cook could serve it forth.

And, indeed, this may work perfectly well under carefully controlled conditions, but culinary science does not take into account the 5-year-old who spends 10 of those 30 minutes whirling the oven dial down to 200 degrees and then spinning it forward to 500 before finally returning it to its proper place and trotting off to play. Nor does it bargain on an oven thermostat that is blowing hot and cold, nor a meat thermometer that has its tip resting on the bone running through the center of the meat.

And, worse than all the rest, it does not allow for how much of the information, passed along in the name of science, is wrong. Harold McGee does take that into account and, in a thoroughly charming and extremely useful new book -- "The Curious Cook" (North Point Press, $19.95) -- he explores and challenges the kitchen lore that we all accept as culinary gospel.

Most cookbooks instruct the cook to sear meat before cooking it. The theory is that this snaps the outer cells closed, forming a crust that holds the juices inside. Ergo, meat that has been seared is moister than meat that has not been seared.

Logical and, as McGee proves in a series of tests, wrong. The juices run just as easily from seared meat. "The searing myth offered a comforting sense of control: Begin with a dose of high heat and you're guaranteed a succulent piece of meat," he writes. "That control turns out to be illusory. On the other hand, if searing caused any great harm, cooks would have seen through the myth long ago."

McGee also passes on another discovery: When oil spits from a hot frying pan, we are not being attacked from below as we would expect, but from above. Most of the hot oil is going straight up into the air and catching us on its way down.

McGee learned this when, after a session at the frying pan, he found that it was the inside of his glasses that were splattered with oil, not the outside.

He summarizes his experiment: "When a bespectacled cook fries food, more oil droplets collect on the inner surface of the lens than on the outer surface. This happens because most of the spatter rises high in the air and falls from above. Since cooks always look down at the stove top, the inner surface of the lens is exposed to this oily rain, which continues for some time after the cooking is over. A baseball cap does a good job of protecting glasses from the fallout of frying."

This summary does not fully capture the charm of an essay that ranges from the origin of the chef's toque to Count Rumford, whose place in kitchen history is secured by his designs for stoves and coffee pots, but who, McGee writes, began his cookery career in dubious fashion. "British soldiers under his command on Long Island used tombstones from a churchyard to build the camp oven, and sent the local citizens loaves of bread with the inscriptions for their deceased relatives baked backward into the crusts."

On the advice of McGee, the chef no longer will bother adding boiling water to finished mayonnaise to stabilize the sauce , but might instead try his recipe for a low-cholesterol mayonnaise using frozen egg yolks.

There is an entire essay on the oft-offered instruction to bring to a boil, and then turn the pan down until the liquid simmers. And the gardener who has been tolerating the tall and intrusive Helianthus tuberosus in the vegetable plot because the root is the Jerusalem artichoke will probably get rid of the thing forever after reading of Harold McGee's futile attempts at "Taking the Wind Out of the Sunroot."

McGee's "The Curious Cook" provides a useful and enjoyable lesson for every one of us: When we lean on science it should be in aid of our senses, not in lieu of them.