William E. Prall was a prolific inventor. His first patents were for pneumatic railway signals, and he later invented a compressed air streetcar propulsion system which was tested in New York City.

He also invented a superheated water district heating system that was demonstrated in New York City in 1880. Theodore N. Vail agreed to finance the Boston Heating Company, which ran for about 20 months before the return pipe corroded. A history of all this, plus a pamphlet from Prall's superheated water company will be placed here soon.

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