What entices people to gather the second Friday of the month in Palo Alto to do English Regency dances?

There's the nimble elegance of the steps, of course. And how many places do you get to wear that Empire-waist gown you sewed yourself?

But let's not forget the math. On one level, says Alan Winston, these dances are all about geometry.

"You're going through patterns on the floor. It's got a lot of appeal for math-science-logic-computer people," says Winston, a computer systems administrator and seasoned dance caller. "It's a great gateway for people who live in their heads to get out and be social."

Social it certainly is. The dance parties, held by the Bay Area English Regency Society at St. Mark's Episcopal Church, attract a friendly crowd. Dancers pair up for waltzes and line up for longways dances, in which couples face each other and progress along their lines. The parties focus on choreography from Jane Austen's lifetime.

The evenings typically attract a dozen to two dozen couples -- and the crowd is much less one-sided than you'd expect, Mountain View regular Christina Bertani says.

"This is a dance for engineers, so we get a great turnout of men," she says.

Many of the dancers are also history buffs who enjoy the early-19th-century ambiance.

"It was such a unique era. Women had a little more freedom. They could go out without chaperones. Some could even run their own businesses," says Theresa Eacker, another regular dancer from Mountain View.

In the ample church room, the floor gleams under cozy light and the live music feels inviting. Pianist William Allen plays traditional country dance tunes with James Langdell on clarinet and recorder. Langdell's chair is surrounded by canvas Trader Joe's bags packed with sheet music.

Dance attire ranges from jeans to skirts to full period garb. One man sports a top hat, and some women have stately up-dos and dresses. (There are more costumes than usual tonight because a reporter is on hand; many people save their period dress for the society's special balls, such as the Cyprians' Ball coming up this Saturday.)

Winston presides over it all. As caller, he lets the group know the steps before a dance begins. Once the music starts, too, there are plenty of experienced dancers ready to kindly point a newcomer in the right direction.

Clearly well-versed in the period's history, Winston is also quick to say when a dance is historically accurate or when it has modern choreography created in the manner of the era.

He first became enamored with the dances in 1978 at, of all places, a science fiction convention. Winston says the science fiction community contains many fans of Georgette Heyer, who wrote "scrupulously researched" novels set during the Regency period. Even now, he regularly leads Regency dancing at the BayCon science fiction convention in the Bay Area.

Winston danced in Los Angeles for several years until moving to the Bay Area in 1985. Here, he had trouble finding fellow enthusiasts, so he co-founded the Bay Area English Regency Society with Vanessa Schnatmeier at the end of that year.

Winston has also broadened his repertoire from just Regency dances to mainstream English country dance as a whole. He has called balls in many places, including Colonial Williamsburg in Virginia.

But despite his expertise, he emphasizes that beginners are always welcome at the Palo Alto events. The steps are usually not physically demanding, and if many beginners attend an evening he'll tailor his dance choices accordingly.

That openness was part of the appeal for Christina Bertani and her husband, Chris, when they started attending a couple of years ago.

"You can come in at a basic level and you aren't going to ruin anything," Christina says from a bench in the dance room where she -- very pregnant -- is taking a well-deserved rest. "Once you learn the basic dance vocabulary, it's easy to ramp it up."

Bertani smiles as she watches sets of couples dance, passing from one partner to another. Nearly everyone is beaming.

"You see why they liked this in Jane Austen's time," she says. "Lots of chances to flirt." Indeed, many people here tonight say they enjoy Regency dance because you feel you're dancing with the entire group.

When the dance ends and Winston begins teaching another one, musician James Langdell gets a quick breather. He displays recorders of varying sizes; with music that repeats its verses over and over during the dance cycles, he switches instruments to keep things lively.

"I've been playing with Alan for 20 years," he says.

Then it's on to "George Washington's Favourite Cotillion," an 1808 tune. Winston calls the dance: "Heads face partners and step back, while sides move in to form lines of four on the sides..."

Presently, everyone takes a break, and Chris Bertani comes over to chat with his wife. He's a standout in a Royal Navy costume rich with gold braid, his hair neatly tied back in a narrow ponytail. He sewed his uniform himself, and estimates it took about 100 hours.

Winston, too, is resplendent in a wine-colored coat with tails, and lace ruffles around his neck. The lace had true period inspiration: He found the style in a portrait gallery in Williamsburg.

Still, he's not above admitting anachronisms in his wardrobe.

"My waistcoat and tails are actually Victorian," he says conspiratorially, then adds, "I bought them on eBay for $15."

What: Dance parties held by the Bay Area English Regency Society

Where: St. Mark's Episcopal Church, 600 Colorado Ave., Palo Alto

When: 8-10:30 p.m. on the second Friday of the month, September through November and February through July.

Cost: $8

Info: Go to http://www.baers.org .