The next time your grandmother predicts a rainstorm because her rheumatism is acting up, pay attention.

And when someone tells you he can "smell" a rainstorm, don't write him off. According to physicist George Freier, weather proverbs often contain more than a grain of truth.

In the days before satellite pictures of advancing cold fronts and Accu-Weather reports people kept tabs on the weather by keeping an eye on the sky and watching wildlife. They put their observations into weather proverbs such as "Red sky at morning, sailors take warning. Red sky at night, sailor's delight."

Freier, author of "Weather Proverbs" (Fisher Books, $9.95), says these phrases should not be dismissed as superstitious bunk. The University of Minnesota emeritus physics professor tested the scientific validity of more than 400 sayings, rhymes and poems handed down by weather watchers as diverse as Roman statesmen, ancient Portuguese navigators, American Indians and Mississippi River barge captains.

"The history of meteorology pretty much starts with weather proverbs," says Freier. "In the development of civilization, one of the first things people needed to learn was when to plant and when to reap. They marked those times by weather proverbs. 'When the crane begins to migrate, it's time to start your planting.' 'When the thistle blooms, it's the middle of summer,' and so on."

Freier's fascination with weather proverbs dates to his boyhood days in western Wisconsin. His family's farm, situated on a hilltop, seemed to attract more than its share of tornadoes and tree-splintering lightning strikes.

"Growing up on that farm, I became interested in big storms and lightning," he says. "I also noticed that farmers, either after church or on Saturday afternoons drinking beer in town, always talked about the weather in terms of weather proverbs. The old guys who knew the most proverbs seemed to be the most prosperous, so I thought there must be some truth to these things."

Years later, armed with his physics training, Freier began analyzing the proverbs he'd heard as a youngster and continued to pick up in everyday conversation. He also searched for proverbs in back issues of the Old Farmer's Almanac, history books, classical literature and other reference works.

He discovered that many proverbs accurately describe -- albeit in a homely fashion -- the movement of weather fronts and changes in barometric pressure, temperature, air stability and wind speed that combine to dictate weather. Some examples:

"Birds flying low, expect rain and a blow." Birds prefer to fly in areas of optimum air density. When the barometric pressure is low -- a sign of an arriving weather system -- that density is nearer the ground. Thus, birds flying lower to the ground may suggest inclement weather is on the way.

"When your joints all start to ache, rainy weather is at stake." As the barometric pressure rises or drops, the human body adjusts internally. This mechanism keeps the body from collapsing or exploding in reaction to changes in external pressure. When barometric pressure falls, gases dissolved in bodily fluids are released as bubbles. Those bubbles can irritate nerve impulses, particularly in joints and wounds, causing aches, itching and other forms of low-grade pain.

"Do business best when the wind's in the west." High pressure systems, rotating clockwise as they move across much of North America, tend to produce westerly winds. Under conditions of high barometric pressure, gases are absorbed one molecule at a time by fluids in the body, causing none of the discomfort associated with bubbling gases escaping under low pressure. The proverb suggests that people may feel most congenial during periods of high pressure.

"If the rooster crows on going to bed, you may rise with a watery head." Like humans, animals can experience the irritation caused by falling barometric pressure, often a precursor to precipitation. "The idea that birds sing because they're happy is not right," Freier says. "Birds sing because they're declaring their territorial rights, and I think they tend to declare those rights more when they're not feeling so good." Related proverbs cite crowing ravens, cackling geese, hooting owls, braying donkeys and restless pigs as still other zoological harbingers of rain.

"Trout jump high when rain is nigh." The same drop in barometric pressure that creates bubbles inside a rooster can activate gas at the bottom of a lake or stream. As the barometer falls, gas bubbles formed by decaying plants begin floating to the surface, carrying along plant particles and insects. As small fish feed on the rising material, larger fish become active, feeding on their smaller prey. Foam on the surface of a river or stream is yet another sign that barometric pressure is falling, says Freier.

"Flowers smell best just before a rain." When moist, the aromatic molecules that stimulate our sense of smell cling more easily to surfaces inside the nose. As the relative humidity, or moisture content, of the air increases, those aromatic molecules collect a layer of water. Increased humidity also improves the likelihood of rain. Thus the odors of flowers, tobacco pipes, manure piles, ditches and ponds may seem more intense before a rain.

That same hydration of aromatic molecules, Freier says, affects animals and insects as well. Ants, for example, communicate through scents called pheromones. When one ant finds food, it will lay a scent trail back to the colony for others to follow. Based on that observation, the following proverb apparently was formulated: "Expect stormy weather when ants travel in a straight line; when they scatter all over the weather is fine."

"When doors and windows start to stick, it will probably rain." When the relative humidity is high, water may condense inside the cellulose fibers of wood, causing the fibers to expand. Sailors also may find that knots in ropes grow tighter before a rain.

"Red sky at night, sailor's delight; red sky at morning, sailors take warning." This proverb makes sense for sailors near the equator, where weather systems move from east to west. In the tropics, a red sky at night means that water particles in a storm system are refracting the colors within sunlight, scattering short-wavelength blue light and allowing longer-wavelength red light to dominate. Because that weather system is moving from east to west, it's headed away from the observer.

In the northern latitudes, Freier says, a more appropriate proverb is "Rainbow at night, sailor's delight; rainbow at morning, sailors take warning." Rainbows appear on the opposite side of the sky from the sun. A rainbow at sunset indicates the rain through which the sun is shining is headed east, away from the observer.

Because weather is caused by many variables, Freier stresses that "one proverb does not the weather make." He recommends, instead, that people wanting to use proverbs to make forecasts search for as many signs as possible as they observe changes in the animals, people and environment around them.

Steve Harned, a meteorologist at the National Weather Service in Silver Spring, agrees with Freier that weather proverbs have a basis in the physics of the atmosphere. "They're around because someone over a period of time noticed the correlation with certain things they were observing. I think most proverbs are based on some fact of the atmosphere."

Given today's frequent radio and television weather broadcasts, and the National Weather Service's network of sophisticated tracking equipment, Freier concedes, the average person's reliance on weather proverbs is not nearly what it once was.

Still, he says, there remain those instances -- vacations, camping and hiking trips, boating excursions -- when the only tool available for evaluating the weather is one's ability to observe nature, along with a rudimentary understanding of weather, passed on through the ages in the form of proverbs.

"Weather information does not have to cease when we're in the woods if we know how to make and use a few observations of our own," Freier writes. "Many things in nature are more sensitive to weather than we are. If we observe the reaction of these informers ... we can learn a lot more about weather changes."