The inventive ingenuity of others brought in time better and more economical incandescent lamps. From the filaments of bamboo fiber the next step was to filaments of cellulose in the form of cotton, duly prepared and carbonized. Later (1905) came the metalized carbon filament and finally the employment of tantalum or tungsten. The tungsten lamps first made were very delicate, and it was not until W. D. Coolidge, in the research laboratories of the General Electric Company at Schenectady, invented a process for producing ductile tungsten that they became available for general use. The dynamo and the central power station brought the electric motor into action. The dynamo and the motor do precisely opposite things. The dynamo converts mechanical energy into electric energy. The motor transforms electric energy into mechanical energy. But the two work in partnership and without the dynamo to manufacture the power the motor could not thrive. Moreover, the central station was needed to distribute the power for transportation as well as for lighting. The first motors to use Edison station current were designed by Frank J. Sprague, a graduate of the Naval Academy, who had worked with Edison, as have many of the foremost electrical engineers of America and Europe. These small motors possessed several advantages over the big steam engine. They ran smoothly and noiselessly on account of the absence of reciprocating parts. They consumed current only when in use. They could be installed and connected with a minimum of trouble and expense. They emitted neither smell nor smoke. Edison built an experimental electric railway line at Menlo Park in 1880 and proved its practicability. Meanwhile, however, as he worked on his motors and dynamos, he was anticipated by others in some of his inventions. It would not be fair to say that Edison and Sprague alone developed the electric railway, for there were several others who made important contributions. Stephen D. Field of Stockbridge, Massachusetts, had a patent which the Edison interests found it necessary to acquire; C. J. Van Depoele and Leo Daft made important contributions to the trolley system. In Cleveland in 1884 an electric railway on a small scale was opened to the public. But Sprague's first electric railway, built at Richmond, Virginia, in 1887, as a complete system, is generally hailed as the true pioneer of electric transportation in the United States. Thereafter the electric railway spread quickly over the land, obliterating the old horsecars and greatly enlarging the circumference of the city. Moreover, on the steam roads, at all the great terminals, and wherever there were tunnels to be passed through, the old giant steam engine in time yielded place to the electric motor.