“Washington has retreated to the air-conditioning,” R. Scott Stephenson, the president and chief executive of the Museum of the American Revolution, which owns the original tent, confirmed in an interview.

The heat has played havoc with plans in Philadelphia, the birthplace of the Declaration of Independence. Its big parade, planned for Friday, was canceled only hours before it was set to start.

Some participants carried on anyway. A chapter of the Sons of the Revolution from Loudon County, Va., invited people to climb on its parked float to sign a reproduction of the Declaration and ring a miniature Liberty Bell.

A high school marching band from Tulsa, Okla., one of 50 from around the country scheduled for the parade, ran through its moves on Independence Mall, as a contingent of Minutemen re-enactors from Massachusetts marched by, sweat stains spreading on their uniforms.

Shawn and Joe Hersey-Massana, two self-described semiquincentennial nerds, had come down from Manchester, N.H., a part of their mission to attend most of the major re-enactments across the Northeast during the run-up to this year’s celebrations.

Shawn was wearing a silver brocade jacket and breeches that were more “Bridgerton” than Ben Franklin. “I’m actually dressed more like George III,” he said. “But nobody realizes it.”

Some long-running July 4 rituals are expected to continue as normal. Bells across the city are still set to start ringing at noon, to mark the symbolic moment when the Continental Congress voted to approve the Declaration.

And there will be a gentle tapping of the real Liberty Bell, by 13 children descended from the original signers of the Declaration. The bell has not been rung since 1846, when it developed its famous crack.

For the record, the temperature on July 4, 1776, topped out at a pleasant (and resonant) 76 degrees, according to Thomas Jefferson’s weather log. But swampy summers were a problem for the founders.

In late June 1778, at the battle of Monmouth, in New Jersey, many of Washington’s men fell down dead from the 100-degree heat. That night, the general didn’t bother having his field tent set up.

“Washington and all the dudes, they just collapsed and slept under a big oak tree,” Stephenson said.