High above all the merriment and learning of the Please Touch Museum, in the chamber between the inner and outer domes that cap Memorial Hall, you can't hear any children playing. The only sound is a distant train whistle - and, at certain inopportune times, flowing water.

Once, when the museum was rented for a wedding, building engineer Hosea Brawley had to go up to the chamber and balance buckets on cast-iron beams to catch the leaks. Despite undergoing a recent extensive renovation, Memorial Hall has suffered damage to both the plaster work and the floor from water intrusion.

The dome has almost always leaked, says architect Philip E. Scott, of KSK Architects Planners Historians Inc. In fact, his firm has uncovered research showing that rain seeped through the dome only months after the building opened as one of the principal structures of the 1876 Centennial Exposition. "When it rains outside," says Scott, "it rains in here."

But if the exposition about cutting-edge 19th-century technology and engineering couldn't stanch the flow, the 21st century will try to do better. In the next few weeks, an elaborate cubed-scaffolding system will begin going up around the Beaux Arts crown on the city-owned building in Fairmount Park. Broken glass will be replaced. A flexible, translucent layer - a liquid product called Sikalastic 621TC - will be applied over the 8,000-square-foot surface of the outer dome. The metal parts of the dome will be treated with the liquid and two woven synthetic fabrics, the glass just the liquid.

The downside: Once applied, there is no feasible way to remove the system. Generally, in historic preservation, reversible materials are preferred, says Theresa Stuhlman, preservation and development administrator for the Parks and Recreation Department. But the Historical Commission gave its approval just the same in September 2013.

Said Stuhlman: "The consensus was, given all of the history of waterproofing problems at the building and the fact that it's not feasible to construct an entirely new dome system, that the parties were willing to take a pretty dramatic step in applying a product that we think is going to stop the issue. It was a judgment call."

Technically, said Scott, "it is reversible in that we aren't damaging historic fabric. But it's not feasible to reverse. We are committing to subsequent campaigns of recoating."

The sealant will replace the previous system, which did not attempt to keep water from seeping through the outer dome, but, rather, managed the water getting in - and not very well. Like a grown-up version of the water play areas for children in the museum, a system of plastic sheets and gutters caught most of the water and funneled it out onto the roof.

The restoration project promises visual improvements, as well.

Part of the previous system is what's called "the diaper" - panels of white plastic sitting atop the inner dome, leading water down into a gutter. That plastic sheet has been keeping out not just water, but also light, so when the new system is in place, the Please Touch will take off the biggest diaper in the place and welcome more light in the Great Hall below.

The financially beleaguered museum - currently renegotiating $60 million in debt owed to bondholders - would hardly seem to be in a position to pay for the renovation. And, in fact, it is not. The budget for the project is $1.125 million; $1 million is coming from the city's capital budget, and $125,000 through the office of Councilman Curtis Jones Jr.

This is considerably less money than the previously contemplated $6 million plan to take apart and reassemble the dome.

The current lighting system, which makes the building a familiar nighttime sight to drivers on the Schuylkill, will be replaced with a system using what Scott calls a "warm-white" LED color. The inner dome - the one visible from inside the building - will stay as is.

Memorial Hall is a shadow of its former self in some aspects. The enormous eagle statues that used to keep watch atop the building are gone. The statue on top, Columbia, needs attention. She is actually the third structure to occupy that perch after an original Columbia and a cupola had turns. "We will re-anchor Columbia," said Scott, "which shifted about three years ago during a summer storm."

Columbia, plus the four allegorical statue groupings just beneath the dome, will be restored with fiberglass and zinc patching. "They are all zinc, and we're going to be cleaning them down to bare metal, then doing the repairs to make sure there are no tears, and removing any of the corrosion," said John Carr, principal conservator of Materials Conservation. Getting the statuary to be watertight is important, he said, "to make sure they not only look good, but also because they function as part of the roof system."

In other words, if the statues leak, the roof leaks. The hope is that the new system will provide at least 20 leak-free years. "We've had a sample area of it up for two years, and it is not letting in any water," said Scott of the dome's trial Sikalastic membrane, which expands and contracts as the temperature changes.

Of course, success has been declared before in the battle to keep out the elements at Memorial Hall. A new system was put in place to keep water out when the building was occupied by the Philadelphia Museum of Art.

"The experiment proved perfectly successful," the museum reported in its annual report for 1882.