early 1930's cast bronze sign plaque salvaged from a sprague multiple poster device invented by frank g. sprague. the novelty device would be used to display multiple lithographic posters and other advertising media with a large window opening. frank julian sprague was an american naval officer and inventor who contributed to the development of the electric motor, electric railways, and electric elevators. he became known as the "father of electric traction". in 1883, edward h. johnson, a business associate of thomas edison, persuaded sprague to resign his naval commission to work for edison. he did important work for edison, including correcting edison's system of mains and feeders for central station distribution. in 1884, he decided his interests in the exploitation of electricity lay elsewhere, and he left edison to found the sprague electric railway & motor company. by 1886, sprague's company had introduced two important inventions: a constant-speed, non-sparking motor with fixed brushes, and a method to return power to the main supply systems of equipment driven by electric motors. his motor was the first to maintain constant speed under varying load. his method of returning power to main supply systems was important in the development of the electric train and the electric elevator. sprague's inventions included a system on streetcars for collecting electricity from overhead wires. 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. the company developed floor control, automatic elevators, acceleration control of car safeties and a number of freight elevators. sprague then sold his company to the otis elevator company in 1895. 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. in the multiple unit system, each car of the train carries electric traction motors. by means of relays energized by train-line wires, the engineer (or motorman) commands all of the traction motors in the train to act together. sprague's first multiple unit order was from the south side elevated railroad (the first of several elevated railways in locally known as the "l") in chicago, illinois. this success was quickly followed by substantial multiple-unit contracts in brooklyn, new york and boston, massachusetts. from 1896 to 1900 sprague served on the commission for terminal electrification of the new york central railroad, including the grand central terminal in new york city, 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. along with william j. wilgus, he designed the wilgus-sprague bottom contact third rail system used by the railroads leading into grand central terminal. during world war i, sprague served on the naval consulting board. then, in the 1920s, he 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.