Frank Sprague
Franklin Julian Sprague (1857–1934) was an American inventor who contributed to the development of the electric motor, electric railways, and electric elevators. His contributions were especially important in promoting urban development by increasing the size cities could reasonably attain (thanks to better transportation) and by allowing greater concentration of business in commercial sections.
He graduated from the United States Naval Academy in 1878. During his ensuing naval service he invented the inverted type of dynamo and installed the first electric call-bell system on a United States Navy ship.
In 1883 E. H. Johnson, a business associate of Thomas Edison's, persuaded Sprague to resign his commission to work for Edison. Although Sprague did important work for Edison, including correcting Edison's system of mains and feeders for central station distribution, he decided his interests in the exploitation of electricity lay elsewhere, and in 1884 he left Edison to found the Sprague Electric Railway & Motor Company.
By 1886 Sprague's company had introduced two important inventions: a constant-speed, nonsparking motor with fixed brushes, and a method to return power to the main supply systems of equipment driven by electric motors. His new motor was the first to maintain constant revolutions per minute under different loads. It was immediately popular, and was endorsed by Edison as the only practical electric motor available. His method of returning power to main supply systems was important in the development of the electric train and the electric elevator.
In 1887 Sprague installed the first large electric railway system in Richmond, Virginia. By 1889 one hundred and ten electric railways incorporating Sprague's equipment were begun or planned. In 1890, Edison, who manufactured most of Sprague's equipment, bought him out, and Sprague turned his attention to electric elevators.
in 1892 Sprague founded the Sprague Electric Elevator Company, and with Charles R. Pratt developed the Sprague-Pratt Electric Elevator. This elevator ran faster and with bigger loads than hydraulic or steam elevators, and 584 elevators had been installed worldwide. Sprague then sold his company to the Otis Elevator Company.
Sprague's experience with elevator control led him to devise a multiple-unit system of electric railway operation, which accelerated the development of electric traction. From 1896 to 1900 Sprague served on the Commission for Terminal Electrification of the New York Central Railroad, including the Grand Central Region, where he designed a system of automatic train control to ensure compliance with trackside signals. He founded the Sprague Safety Control & Signal Corporation to develop and build this system.
In the 1920s, Sprague devised a method for safely running two independent elevators, local and express, in a single shaft to conserve floor space. He sold this system, along with systems for activating elevator car safety systems when acceleration or speed became too great, to the Westinghouse Company.
The effect of Sprague's developments in electric traction was to permit an expansion in the size of cities, while his development of the elevator permitted greater concentration in cities' commercial sections and increased the profitability of commercial buildings.
Sprague was awarded the gold medal at the Paris Electrical Exhibition in 1889, the grand prize at the St. Louis Exhibition in 1904, the Elliott-Cresson Medal in 1904, the Edison Medal of the American Institute of Electrical Engineers in 1910, the Franklin Medal in 1921, and the John Fritz Gold Medal, posthumously, in 1935.
