Bear with me while I report that the price of copper during the past decade quadrupled on the New York Mercantile Exchange.

That far-flung fact may have guided the thinking (using the term loosely) of the local thieves who sneaked onto the grounds of the Arlington Historical Society last month and ripped off three 40-foot copper downspouts.

Given their importance to keeping water out of the historic Hume School-built in 1891 on Arlington’s South Ridge Road-such artifacts are hardly frills. “It’s a financial hit” to a self-funded organization with a $88,000 treasury, says society president Tom Dickinson. Replacement will cost $2,500-$3,000 (though the group carries insurance with a $1,000 deductible).

Then there’s the problem of whether to order authentic copper or cheaper modern material that, while less tempting to thieves, might be frowned upon by Arlington’s Historical Affairs and Landmark Review Board, which has authority over the county-owned property.

Such are the travails of my favorite local membership group, to which I’ve paid dues for 12 satisfying years. For an annual bargain of $25, the group that has stewarded county heritage since 1954 provides exhibits, a bookstore, a speakers program, a newsletter and an annual magazine whose writers, I can vouch, contribute for love and not lucre.

The society’s banquets have featured talks by former NPR host Bob Edwards, Weekly Standard editor (and Arlington native) Fred Barnes andWashington Post local columnist John Kelly.

Just last week I caught its terrific lecture documenting the black-owned businesses in Arlington that sprung up during the era of forced segregation, showcasing research by George Mason University geographer Nancy Perry.

The labor to keep AHS headquarters open to visitors (weekends from 1-4) is all-volunteer. Unlike counterparts in Alexandria and Fairfax, the Arlington history boosters get no public funding.

So, like many nonprofits in not-quite-post-recession America, the society is scrambling. It copes with the Hume school’s rickety HVAC system. Its prized possession, the mid-18th-century home called the Ball-Sellers House (near Route 50 and Carlin Springs Rd.) that is Arlington’s oldest, suffers from rainwater pooling around its stone-and-mortar foundation. (A $25,000-$30,000 repair project is out for bids.)

The AHS membership roster of 350 is shrinking, and the search is on for young blood, Dickinson says. Dues, stable for a decade, make for “a diminishing revenue stream and an unsustainable funding model over the long run.”

The society needs a Webmaster and a building manager. This year marks the 10th anniversary of the 9/11 attacks, but there’s inadequate space to display the Pentagon’s artifacts.

Next year will mark the 200th anniversary of the War of 1812, an event, Dickinson reminds me impressively, that caused the original Constitution and Declaration of Independence to be taken by State Department employees to Chain Bridge where, after being suspended in linen sacks from the chain trusses, were moved safely to a nearby mill.

And like much of the nation, Arlington is just getting started on the 150th anniversary of the Civil War.

Michael Leventhal, Arlington’s historic preservation coordinator, predicts the review board will likely allow the society to order downspouts of a nonprecious metal and then paint them the historic color. “We’re not colonial Williamsburg, we’re a living city,” he says.

Memo to thieves: It’s a question of values. The custodian of an historic community’s heritage, or a few bucks for pilfered copper?

Charlie Clark may be e-mailed at cclarkjedd@aol.com