The electric chair as a method of execution was promoted by Thomas
Edison, as an effort to show how dangerous AC power was?

This was not exactly the case although there were elements of safety involved.
Around 1886, the New York State Legislature set up a commission to check into 
"electrical" alternatives for executing criminals.  A patent for the electric 
chair was filed by Harold Brown in New York State (son of a gun!) by 1887.  
At that time, Brown was working with the chief researcher at Edison's lab in 
Menlo Park, Dr. A.E. Kennelly.  They tested it by zapping around fifty cats 
and dogs.  Supposedly all were strays (yeah, right, where's the SPCA when you 
REALLY need 'em?).

Anyway, the commission was skeptical and so Brown and co. fried a cow in 
their face.  To drive the point home, he then fried a horse.  New York
Governor David Hill signed a bill making the electric chair a legal way to 
execute criminals on June 4, 1888.  To convince officials and the public of 
the benefits of electrocution, Brown took his dog and pony show on the road.  
In Albany, he electrocuted an orangutan.  In a scene predating Pepsi 
commercials by a hundred years, its hair caught fire.

All was not well though.  Northeast electric companies were opposed to
electrocution as a means of death because it might spark further public
fear of the dangers of electricity.

At this time, Edison had been trying to sell the industry on his DC system
for transmitting power.  His rival, George Westinghouse, was pushing his 
"more efficient, reliable, and easier to transmit" AC system.  The Chair
worked on AC so Edison saw a means to try to scare the industry off of
using Westinghouse's method and to this end, offered the use of his labs
to Brown to perform experiments.  At any rate, Edison lost out on this
one and the industry adopted AC as a standard.

So safety was involved, but Edison was more interested from a business 
motive rather than an altruistic one.  Edison went on to have great
fame (and unfavorable comparisons to Tesla on AFU).  Westinghouse founded
a company whose tradename in lamps is now owned by the Dutch.

As it turns out, the use of the electric chair (esp. in the beginning)
did show how dangerous AC current was to the successful and humane
execution of criminals.

The above is documented in _Panati's Extraordinary Endings of Practically
Everything and Everybody_.  ISBN:  0-06-096279-8.

Terry "What's this switch for?  Ouch!" Chan