included a meter to determine the
current actually consumed. The success of the system was complete, and
as fast as lamps and generators could be produced they were installed
to give a service at once recognized as superior to any other form of
lighting. By 1885 the Edison lighting system was commercially developed
in all its essentials, though still subject to many improvements and
capable of great enlargement, and soon Edison sold out his interests in
it and turned his great mind to other inventions.

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