If the airplane passenger sitting next to you has a tube leading from the ventilator over his head to an instrument on his lap, you can be sure he's Vincent J. Schaefer, ''father of rainmakers.''
Who else would be busily measuring air quality in the upper atmosphere while other passengers are snoozing, staring out windows, doing crossword puzzles, or watching a movie?
He explains: ''I make it a point to carry my equipment with me when I travel so I can measure things whether I am going for that purpose or not.''
This is a sample of the industry and homespun practicality that has characterized Dr. Schaefer's meteoric rise from a high-school dropout to one of the world's most distinguished atmospheric scientists. In 1946 he startled the world by being the first to discover a feasible method of seeding clouds. Now, even in so-called retirement, this self-educated ''snowflake scientist'' is still up in the air, his interest in the atmosphere continually expanding.
Once on a trip home from London, he recalls, the pilot came back to talk to him. (After all, it isn't your run-of-the-runway passenger who samples incoming air to find out what is going on outside.)
''I guess there's an airplane ahead of us,'' Dr. Schaefer remarked cooly. ''No way,'' the captain replied. ''We have our radar going. There is nothing ahead of us. The closest airplane is 60 miles to the south.''
Dr. Schaefer chuckles as he recounts what happened next. In a little while the captain returned. ''You were right,'' he said sheepishly. ''We were overtaking a Comet airplane that wasn't supposed to be there.''
How did this affable sky bug from the little village of Rotterdam, N.Y., know that? ''Because the upper atmosphere is very clean,'' he says in an interview in his home near Schenectady. ''Normally the indication I get up there is that there are hardly any particles at all. So when I suddenly begin getting 10,000 particles (per cubic centimeter), I know there's something very different going on.''
When he deboards, he has a pocketful of air-quality measurements that he shares with scientists, societies, and libraries throughout the atmospheric field.
With his fine-particle measuring instruments, it is nothing unusual for him to detect the invisible plume of a power plant 50 to 75 miles away.
While on a geological expedition down the Colorado River, he announced that a power boat was coming downstream 20 minutes before it appeared. ''Its pollution plume was sliding down the Grand Canyon's lower air faster than the boat was,'' he says.
When Dr. Schaefer discovered how to cut holes in clouds by seeding them with dry ice (solid carbon dioxide), he sprang to fame overnight as a weather moderator. He was then an unknown research scientist at the General Electric Corporation in Schenectady, working with Nobel Prize-winning scientist Dr. Irving Langmuir.
What he was searching for was some kind of material which, when sown in ''supercooled'' clouds, would trigger them into snowing or raining. Supercooled clouds have temperatures below 32 degrees F. but are made up of water droplets that are still liquid.
It was while he was experimenting with his cold chamber, used to produce artificial clouds, that he stumbled upon the answer. ''On a very hot July day,'' he says, ''my cold chamber wasn't working too well. To cool it off, I put some chunks of dry ice into the chamber. The instant they went in, I had my answer. There were so many ice crystals that it made a blue cloud.''
He soon found that only a few tiny fragments of dry ice falling into the chamber were enough to change the fog to ice crystals.
''I immediately went up in a plane and tried a few experiments,'' he says. ''I found it worked every time we had a supercooled cloud.''
The US government saw at once the potential applications of cloud seeding. For five years Project Cirrus, a joint government and industrial effort, explored the possibilities and limitations of the process.
In his new book, ''A Field Guide to the Atmosphere,'' co-authored by John A. Day (Boston: Houghton Mifflin. 1981), the authors record what has happened since then:
''For the first 20 years that the seeding of clouds was conducted, there was much controversy about the reality of its effectiveness in the free atmosphere. It is now generally agreed that it is quite feasible as a way to disperse supercooled fog at airports, to carve holes in supercooled stratus decks, to change the electrical nature of thunderstorms, to increase convection in large cumulus clouds, to reduce hail damage, to increase the snow pack in mountains, and to increase rainfall by 10 to 30 percent where there are substantial amounts of supercooled clouds. . . .
''There is no question that a supercooled cloud can be completely converted to ice crystals by the use of proper seeding techniques,'' the writers unequivocally declare.
But like many other fedral programs today, cloud seeding experimentation has fallen on hard times. Some work is still being done by the Bureau of Reclamation and the National Oceanic and Atmospheric Administration. But the Reagan administration wants to eliminate all weather modification funds from NOAA's budget. Congress may restore some funds for fundamental research, but there is wide agreement that direct efforts to make snow or rain should be put on the back burner. There has been much experimentation and many claims of success in rainmaking. But there is little hard evidence of success so far with the exception of some work in Israel.
For nearly 30 years an irrigation district in California's San Joaquin Valley has tried cloud seeding to increase precipitation. But the practice has become controversial. Some people worry that seeding can do harm as well as good. Some legislatures have imposed limitations on seeding. More of it is going on now in such foreign countries as Chile, Spain, and Greece than in the US.
Dr. Schaefer is no longer directly involved in the issue. But he believes that ''in this country we got off on the wrong foot. Rather than accepting that you could do something with a supercooled cloud, decisionmakers in high places contended that you couldn't.'' Experimental studies of cloud seeding's effectiveness were ill-conceived, he maintains.
For 11 winters Schaefer conducted his own cloud-seeding experiments in Yellowstone National Park at temperatures of -40 degrees F. He led month-long expeditions to what he calls ''this perfect natural laboratory.'' At that temperature, he could make an instant cloud by simply tossing a cupful of water in the air.
Every night a supercooled fog formed over the region because of the hot springs and geysers pumping moisture into the air. Because the atmosphere was so clean, these clouds were always supercooled. ''It was like walking in a cirrus cloud,'' he says. Morning after morning on schedule he caused snow flurries by seeding this supercooled fog.
The project came to a screeching halt when snowmobiles were permitted into Yellowstone. As many as 1,000 were roaring through the snowy wilderness on a single day. Their exhaust so polluted the atmosphere that Yellowstone lost its usefulness for these experiments.
In the meantime, the Weather Modification Association, a private organization he helped form 25 years ago, is pushing for ''sensible'' legislation regulating cloud seeding. By certifying whether a person has the capability to seed clouds , it seeks to protect the public from charlatans.
Though it was his cloud-seeding discovery that brought him international fame , Dr. Schaefer's happiness does not hinge on whether weather modification flies or not. Among his associates in the scientific world, he is known as a Renaissance man with a zest for gathering and sharing knowledge in many fields, of which cloud seeding is only one. That's the story of his life - teaching himself, then teaching others.
His book is an example. One of the Roger Tory Peterson Field Guide Series sponsored by the National Audubon Society and the National Wildlife Federation, it is his distillation of 40 years of sky watching. ''It contains most of the things an ordinary person should know about the atmosphere. It is not a highfalutin book,'' Dr. Schaefer says, smiling. ''It's not aimed at college professors. It's aimed at the general public and the high-school youngster.
''The reason I wrote it was to get people more interested and conversant with the sky.'' Prehistoric American Indians and early American farmers, he says, understood a lot more about the atmosphere than most Americans today. If people understood what they see when they look up, he says, maybe they would have more concern for the beauty of clean sky. This in itself, he believes, could begin to solve the universal problem of atmospheric pollution.
Chasing rainbows and clouds and other natural special effects has taken Dr. Schaefer to the ends of the earth. ''A Field Guide to the Atmosphere'' is richly illustrated with black-and-white and vivid color pictures of spectacular sky events he has witnessed and photographed - many of them taken in his native New York.
The jet stream, Dr. Schaefer points out in the book, is a very important part of the atmosphere. As a rule, this river of air enters the United States over Washington State, wanders across the North American continent, then exits over New England and New York State. This, he says, accounts for the beautiful sunrises and sunsets often seen in the Northeast.
''If a hurricane is coming up the coast and you're concerned whether or not it's going to hit the place where you're located,'' Dr. Schaefer says, ''if there is a jet stream overhead, you can be sure it's not going to come, because the jet stream won't let it. It is such a powerful stream of air, that it deflects it.''
There are directions in the Schaefer book for conducting simple atmospheric experiments: how to set up a cold chamber; how to make and seed a supercooled cloud; how to pick up particles in the atmosphere. (Just fasten a glass slide to a stick, and hold it out a car window while going 40 miles an hour. Then put the slide under a microscope and see if you can detect the nature of the particles and where they came from.)
Dr. Schaefer concedes that ''there is nothing in nature that I'm not interested in.'' The pile of rocks alongside the Schaefers' garage illustrates his interest in everything around him. One could easily mistake them for any other stone wall in this big-sky Mohawk Valley.
A closer look reveals that each rock is numbered, awaiting its turn to be sliced up like baloney by a ravenous diamond-saw rock-cutting machine Dr. Schaefer keeps humming most of the time in the basement workshop of his home.
His motto: ''Your laboratory can be wherever you live.'' Still, it is amazing what a world of wonders this self-taught scientist has found in his own backyard , from the jet stream overhead to boulders underfoot, deposited here tens of thousands of years ago by a mile-high glacier inching across this region's Adirondack Mountains.
Dr. Schaefer has been saving rocks since he was a small boy. He has samples gleaned from all around the world. But again, most of them are from his own region.
''I knew that some day I'd probably be able to cut them to bring out their greater beauty,'' he says. But only recently has he caught the bright idea of slicing them so thin that their kaleidescope of colors and designs can be seen in all their vivid hues when held up to the light. He now has 5,000 slices of rocks from more than 200 locations which are neatly stashed away in his busy basement workshop. Their rainbow hues range from real garnets to green serpentine stones.
It was the need of his family's Roman Catholic church for a new stained-glass window that triggered this new hobby. He volunteered to make it in memory of his parents.
The result is the St. James Window: Concentric hexagonals inside a circle symbolize to him the hexagonal snow crystal. The window also contains the outward spiraling shape of the nautilus sea shell, a form associated with the great Italian mathematician Leonardo Fibonacci.
These forms, plus the ''golden sections'' of classic times - rectangles and triangles whose proportions the ancients considered particularly beautiful - recur repeatedly in the mosaic windows he has made for his home, as well as in trays, lampshades, and other decorative pieces he is fashioning these days as gifts for friends.
Dr. Schaefer has always learned by doing. At first this was a matter of necessity. He had hoped to go to college and become a forester. But after two years in high school, he took a job to help his parents support their large family.
Four years later he completed his apprenticeship as a machinist at General Electric and began making instruments for the company's Research Laboratory scientists. He was such a model modelmaker that he caught the attention of Dr. Langmuir. From then on, as one writer put it, he attended ''Langmuir university'' in the Mark Hopkins's sense of a university being a great man on one end of a log and a student on the other.
Vince Schaefer proved to be such an apt pupil that in a short time he had learned so much about the surface chemistry Dr. Langmuir was working on that young shaver Schaefer began doing his own research.
This happy professional relationship continued as each scientist challenged the other. During World War II they worked together to solve critical problems the US faced.
They developed for the US government a gas mask filter to protect troops against a deadly nerve smoke developed by the Nazis; rigged up a device for detecting enemy submarines; invented a way to make artificial fog that covered huge areas to screen troop and ship movements and to protect civilians from air attack.
The US Air Force was losing planes that would fly though supercooled clouds, ice up, then crash. This urgent need to modify supercooled clouds triggered the scientists' search.
The war was over before Dr. Schaefer discovered that dry ice was what he was looking for. Later in '46, Dr. Bernard Vonnegut, another colleague of Dr. Schaefer, found that silver iodide could be used for the same purpose.
This project lofted Dr. Schaefer into a lifetime interest in the atmosphere.
In the mid-'50s he left GE to head up the Munitalp Foundation Inc. In this capacity he issued a grant to the International Meteorological Institute in Stockholm that funded the first studies in acid rain.
Dr. Schaefer's own measurements have subsequently convinced him that acidity in the atmosphere is not just a local problem that fouls his trout-fishing sport in the Adirondacks but is a problem of global dimensions, ''a warning to all of us that we are beginning to overload the atmosphere.''
A big step in solving this problem, he believes, is to obey one of his strictest precepts: Take advantage of opportunities that are available.
By that he means that the world should change the way it makes electricity. Instead of retrofitting 6,000-megawatt electric generating plants that have an efficiency of only 33 percent, ''we should be building many more but much smaller plants of perhaps 150 megawatts that use new techniques and operate at up to 50 percent efficiency, using coal that has been washed of sulfur. This way we would get more efficiency, less pollution, and we would not have to carry electricity hundreds of miles by powerline.''
In 1961, at the request of the State University of New York at Albany, Dr. Schaefer formed the Atmospheric Sciences Research Center, which he headed until he retired in 1976. But he is still continuing consulting work which he began in the 1950s.
Is he some sort of genius that he has achieved so much with so little formal academic training?
From finding Indian arrowheads as an 8-year-old to founding a scientific research center, Dr. Schaefer's approach has been practical. He has been a voracious reader of books, pursued his many interests, taken advantage of every opportunity, and cherished the friendship of what he calls ''worthwhile people.''
''Anybody could do it if they had the desire,'' he says. ''You have to have a sense of wonder and continual curiosity. You have to be aware of what goes on around you. You have to develop what I call 'intelligent eyes.' You have to be intrigued with the world and everything that is in it.''