Engineer's concept of a water powered 'Wheel mill" showing upright grinding wheels,contained a two to four inch layer of gunpowder ingredients. It was essential to maintain a layer of the mixture at all times to keep the wheels from touching the metal trough which would cause a spark, resulting in an explosion. .When the Powder Mills closed in 1905, local residents heaved a sigh of relief.the sleepy villages of Windham and Gorham frequently rocked with the unexpected explosions.