In 1869, across the United States in the hilly metropolis of San Francisco, Andrew Hallidie, a recent immigrant from England, witnessed a horrible accident during a typical damp summer day. A horse drawn streetcar slid backwards under its heavy load. The steep slope with the wet cobblestones and a heavily weighted vehicle combined to drag five horses to their deaths. Years earlier, Hallidie's father had filed the first patient in England for the manufacture of wire rope. Andrew Hallidie had used this technology for designing a suspension bridge in Sacramento and for hauling ore cars out of the underground mines. This accident inspired him to devise a mechanism by which streetcars were drawn by an endless underground cable running slowly in a slot between the rails ,
What is a trolley? The nickname "trolley" has been a common name when referring to the streetcar. It's inventor, Frank J. Sprague, was a former Naval officer who briefly went to work as an assistant to Thomas Edison. Sprague was fascinated with transport mechanisms. His first major invention was a high-power, constant-speed, non-sparking electric motor with applications for industrial machinery. He also devised an improved braking system. In 1884, with Edison's help, he established the Sprague Electric Railway and Motor Company and in 1888 his invention pioneered the first streetcar system powered by electricity.
His system used overhead wires hung between poles installed on either side of the roadway. The current, produced by large steam powered generators, was conducted to the electric motor in the streetcar by a long metal pole on the roof of the streetcar. (diagram here) The "trolley" at the end of the metal pole was the contact point between the vehicle and the electric supply, which slid along the wire to provide power to the motors.
Within two years, he had contracts for 113 street rail systems across the country, designed and built Chicago's elevated "L" electric railway,
and co-invented the "third rail" system for New York's Grand Central Railroad.