During the initial years of electricity distribution, 
Edison's DC was the standard for the United States and Edison was 
not disposed to lose all his patent royalties. During the commonly 
referred to "War of Currents" era, Serbian immigrant Nikola Tesla and 
Edison became adversaries due to Edison's promotion of DC for electric 
power distribution over the more efficient alternating current (AC) 
advocated by Tesla, who patented AC in Graz, Austria. Edison (or, 
reportedly, one of his employees) employed the tactics of misusing 
Tesla's patents to construct the first electric chair for the state 
of New York in order to promote the idea that AC was deadly. Popular 
myth has it that Edison invented the electric chair, despite being 
against capital punishment, solely as a means of impressing the 
public that AC was more dangerous than DC, and would therefore be 
the logical choice for electrocutions. In fact, like most of the 
output of the Menlo Park operations, the chair was primarily invented 
by a few of his employees, in particular Harold P. Brown, while 
Edison supervised their operations. 

Edison went on to carry out a campaign to discredit and 
discourage the use of AC, by what today would probably be 
referred to as FUD. Edison presided personally over several 
electrocutions of animals, primarily stray cats and dogs, 
for the benefit of the press to prove that his system of DC 
was safer than that of AC. Edison's series of animal 
executions peaked with the electrocution of Topsy the 
Elephant. Ironically, Edison was against capital punishment, 
but his desire to disparage AC led to the invention of one of 
the world's most recognizable killing devices.

Many of Edison's inventions using DC ultimately lost to AC 
devices proposed by others: primarily Tesla's polyphase 
systems and other contributors, such as Charles Proteus 
Steinmetz (of General Electric). AC distribution systems 
replaced DC, enormously extending the range and improving 
the safety and efficiency of power distribution. Since the 
1950s, High Voltage Direct Current (HVDC) transmission 
systems have become more common in certain situations. 
HVDC systems are presently used for some specialised 
applications like the underwater interconnection of 
power systems.

In the "War of Currents" era in the late 1880s, Nikola Tesla 
and Thomas Edison became adversaries due to Edison's 
promotion of direct current (DC) for electric power distribution 
over the more efficient alternating current (AC) advocated by 
Tesla.

During the initial years of electricity distribution, Edison's 
direct current was the standard for the United States and 
Edison was not disposed to lose all his patent royalties. From 
his work with rotary magnetic fields, Tesla devised the system 
for transmission of power over long distances. He partnered 
with George Westinghouse to commercialize this system. 
Westinghouse had previously bought the rights to Tesla's 
polyphase system patents and other patents for AC 
transformers.

Work relations

As exemplified by the light bulb story, most of Edison's 
inventions were improvements of ideas by others, achieved 
through a diligent and industrial approach and team-based 
development. He was the undisputed head of the team but usually 
did not share credit for the inventions. He himself said: 
"genius is one percent inspiration, ninety-nine percent 
perspiration." Nikola Tesla, possibly Edison's most famous 
employee and who went on to be a great scientist and inventor 
in his own right, said about Edison's method of problem-solving: 
"If Edison had a needle to find in a haystack, he would 
proceed at once with the diligence of the bee to examine 
straw after straw until he found the object of his search. 
I was a sorry witness of such doings, knowing that a little 
theory and calculation would have saved him ninety per 
cent of his labor."

Frank J. Sprague, a former naval officer, was recruited 
by Edward H. Johnson, and joined the Edison organization 
in 1883. Sprague was strong in mathematics, and one of 
Sprague's significant contributions to the Edison Laboratory 
at Menlo Park was the introduction of mathematical methods. 
Prior to his arrival, Edison conducted many costly 
trial-and-error experiments. Sprague's approach was to 
calculate using mathematics the optimum parameters and 
thus save much needless tinkering. He did important work 
for Edison, including correcting Edison's system of mains 
and feeders for central station distribution. In 1884, 
Sprague decided his interests in the exploitation of 
electricity lay elsewhere, and he left Edison to found the 
Sprague Electric Railway & Motor Company. However, Sprague, 
who later developed many electrical innovations, always 
credited Edison for their work together.

At a meeting in late 1885, of Edison, Edward H. Johnson 
(President of the Edison Illuminating Company), Charles 
Batchelor (Manager of the Edison works) and Nikola Tesla, 
one of the group suggested guessing weights and Tesla was 
induced to step on a scale. Edison guessed that Tesla 
weighed 152 pounds (69 kg), to an ounce. Johnson 
confidentially related to Tesla that Edison could guess 
individuals' weight as he had developed the skill when 
he was employed for a long time in a Chicago 
slaughter-house where he weighed thousands of hogs 
every day