In the 50 years since an Inverness newspaper reported "the appearance of a strange animal or fish in Loch Ness," we have learned to live with such ideas as these: that matter is energy, that atoms can be smashed, that subatomic particles have some attributes associated with particles and others associated with waves, that the soul or "self" is a kind of fractious committee and the unconscious is an arena of turmoil revealed in dreams and elsewhere, that the continents are floating plates meandering around the planet, that Saturn has braided rings of giant snowballs, that the dinosaurs may have died quickly as a result of an environmental catastrophe (for them, not us) caused by a meteor striking Earth, that light is subject to gravity because space is curved near large masses, and that there is a decipherable code of heredity contained in a substance (DNA) common to all living things from turnips to violinists. But it is generally considered beneath serious consideration that a large creature lives in Loch Ness.

Because the "monster" has been good for Scotland's tourist trade, cynics dismiss it as a fabrication. Because a willingness to construe other persons' beliefs as products of neuroses is widely considered a sign of bravery and learning, persons who say they have seen the creature or evidence of it, or who even remain open-minded about it, are said to be manifesting an instinctive human craving for myth, and the hunger of a secular age for mystery, and all that stuff.

Perhaps persons who think Nessie may exist are mistaken. No member of the species has been captured, no remains have been found, no incontrovertible photographic or other evidence has been gathered.

But in 565 A.D., Saint Columba, who brought Christianity to the Scots (who were sore in need of it), saw a beast in Loch Ness. Claimed sightings became more frequent 50 years ago when a road was opened along the loch's western shore. That's when Mr. and Mrs. George Spicer were driving toward London and encountered a "loathsome sight."

The loch is only 24 miles long and a mile wide, but it is so deep it is, in volume, the largest lake in Britain and the third largest in Europe. Therefore, although there have been hundreds of claimed sightings by scientists and laymen, the absence of definitive evidence for the creature's existence can conceivably be due to the fact that the loch has ample room for a reclusive creature to avoid the limelight.

After assessing photographic and sonar evidence gathered in 1972 and 1975, the curator of the Smithsonian's division of reptiles and amphibians said the data "indicate the presence of large animals in Loch Ness." Also in 1975, a curator in the department of vertebrate paleontology at the Royal Ontario Museum said: "There is an unexplained phenomenon of considerable interest." The director of Harvard's museum of comparative zoology said the evidence was "suggestive of a large aquatic animal." Evidence was treated as scientifically serious in the Harvard museum's "MCZ Newsletter" and in "Technology Review" published at MIT.

Peat particles in the murky water make underwater photographs difficult to decipher, but computer-enhancement of photographs at the Jet Propulsion Laboratory in Pasadena has shown the photographic record to be consistent with the sonar record indicating moving objects 20 to 30 feet long. In 1960 an aeronautical engineer filmed what he said was one of the creatures swimming on the surface. The British joint air reconnaissance intelligence center said the film "leaves the conclusion that it (the thing on the surface) probably is an animate object."

A 1976 article in Smithsonian magazine concluded: "There's something in the loch, something big, even though we don't know what." Perhaps that is not so. Perhaps the testimony of individuals and the sonar and photographic evidence can be explained (as has been suggested) in terms of mass suggestion, or a sunken Viking ship, or clouds of gas bubbles, or floating trash, or a decaying stag's head.

But it is curious the amount of faith sometimes needed, and sometimes forthcoming, to maintain a particular skepticism. It is still possible that the story of the Loch Ness creature illustrates the number of ideas people are willing to entertain in order to avoid entertaining one idea that is considered naive or otherwise out of place in polite society.

No metaphysic will come unstuck, no moral code will be refuted, no notion of man's place under the eye of eternity will have to be revised if, say, we someday discover that a species of large prehistoric reptiles got locked in the loch by a geologic accident and has been dining well on Scotch salmon ever since. (Several sightings have been associated with salmon in headlong flight.) But many persons close their minds against many thoughts in order to avoid being thought insufficiently skeptical.

Of course, credulity can be costly, as Stern magazine can attest. But skepticism can be a kind of dogmatic slumber, and the world has much to lose from an atrophied capacity for wonder and surprise. Certainly the history of science in this century should serve as a warning against a narrow notion of the possible.