Powder house, mahogany model of a house with a lightning rod
The powder house, which could contain a bit of gunpowder, offers a dramatic demonstration of the efficacy of lightning rods, particularly those with pointed tips, advocated by Franklin. The house is safe when electricity can travel from a cloud to a lightning rod to the ground, but when the circuit is broken, the roof flies off and the walls collapse.
Simpler versions of the powder house were known from the 1750s. Similar models are pictured in the background in Franklin's 1762 portrait by Mason Chamberlin. Harvard College purchased the powder house in 1789; it was probably made in London.