"Always stay in close physical contact with your diving buddy when diving at night," Ray Jarvis said. "I repeat: physical contact. Hold hands, forearms, or keep a hand on your buddy's tank. But don't lose physical contact. We'll be diving with lights, but don't get separated because the lights won't shine much farther than 30 feet."

Jarvis is a diving instructor certified by the National Association of Underwater Instructors. He also manages the National Diving Center on Wisconsin Avenue, and takes both jobs seriously. That's the only kind of instructor or supplier to have.

We were at Haymarket Quarry, a flooded 90-foot hole near Gainesville, Virginia, for our first dive into the dark.

Night scuba is something to get into only after learning the basics well. There are new problems to meet and new skills to learn. Why do it? Well, like the unclimbed mountain, it's there. And the creatures are often more active and interesting then. And besides, it's easier to catch lobsters at night when they're foraging than during the day when they hide.

Jarvis laid out the dive plan: "As soon as we've put on our gear we'll snorkel, in three three-person teams, out to the raft of barrels. I'll take one team at a time down to the platform submerged 10 feet below the barrels. When you get to the platform adjust your B-Cs [buoyancy compensators] so that you're all neutrally buoyant, and then we'll descend to a ledge 40 feet down, circle once around a school bus and a truck down there and then follow the 40-foot contour line back up here where we'll surface. It'll take about 20 minutes."

Diving in the absence of daylight can be disorienting. At neutral buoyancy you neither rise nor sink, just stay put.In daylight the bottom, the bubbles, the surface and the light all tell you which way is up. In darkness or in murky water, there is only the bubbles. But the disorientation is more initial discomfort than danger to someone who's been through a basic course.

Diving in the dark, you should always carry lights and a chemical glow-light to the strap on your mask so you can be found even if the other lights fail.

The first team descended, and 10 minutes later the second went down, leaving Tom, 14, and me bobbing with the barrels in the inky darkness, watching the vanishing lights as the students left the platform.

Ten minutes later a stream of bubbles announced the surfacing of Ray Jarvis.

"You guys ready and okay?"

Sure. Jarvis repeated the dive plan. We air from our B-Cs and sank. At 10 feet the water was colder, and at 40 it was freezing until it warmed to body temperature inside our wet suits.

The bus was a rusting hulk, out of place and somewhat mysterious: evidence of an unknown disaster? Nice-size rainbow trout swan, as we did, in and out of the twisted metal. A plump 12-inch female paused to look at us, backed a few inches and approached again as if to ask if we were lost.

There, 40 feet beneath the surface, was a fish behaving like Robert Frost's little horse that thought it queer to stop without a farmhouse near. GETTING INTO THE SWIM OF IT

This is only a sampling of what's available to the more than 8,000 divers in the area. There are wrecks to explore, lobsters, crabs and fish to catch, spear or photograph, and occasional relics. And every dive provides memories to fill those moments when the workaday world isn't enough.

The place to start is in a classroom at almost any of the area's many dive shops, YMCAs or recreation departments. Most of the shops have sign-up sheets for charter diveboats that go out every fair weekend from May to October -- often to wrecks off Maryland and New Jersey.

A basic course will run from $50 to $75 for about 32 hours of classroom and pool instruction plus three open-water dives. Some shops give students cut-rate rentals. Certification is required by law for the purchase of scuba air in much of the Caribbean and is demanded by most American dive shops.

The basic course teaches how to: clear a leaky mask underwater; equalize pressure inside your sinuses and ears as you go deeper; swim without sinking or rising; get more time from a tank of air; get in and out of the surf and how to "buddy breathe" -- pass one regulator back and forth in case another quits. Most of all you'll learn to relax underwater while breathing canned air and swimming like a fish in a world that is surprisingly easy to get to know.