• several different alternating currents out of phase with each other create a rotating magnetic field that pulls the moving part of the motor around (or pushes it around as two magnets repel each other)
• there are several ways to do this and the simplest (two wire split phase) is less efficient than Tesla's four wire system
  
• see this page for a second level understanding
• Tesla had that theoretical principle but didn't know nearly enough to actually build it
• AC has the advantage (not yet fully understood) that it can be transformed to a higher voltage for transmission with less loss and then back to a lower voltage for use
• AC can be either single phase (two wire) or polyphase (four or more wires)--Tesla's motor in its ideal form required polyphase, but it had no advantages for electric lighting systems
• split phase is a single alternating current modified to act more like polyphase
  

What do we learn in these chapters about Tesla's process of invention:

• Tesla first builds something in his head
• it works in principle but he doesn't have all the practical problems solved--he first used a material for the cores that meant it didn't work at all
• he comes up with quite a lot of patents for different kinds of generators, motors
  

Tesla gets the opportunity to work for the Edison company in Paris
but they aren't yet interested in motors or AC

he got a chance to experiment with actually building an AC motor in Strasbourg in late 1883
discovered that what he imagined in his mind didn't initially work because there were other issues such as using the right materials

Tesla is beginning to look unsuccessfully for a partner to put up money to develop the motor

Tesla's success in improving dynamos (generators) gets him a job with the Edison company in New York (the city does not impress him)

Quits because he doesn't get bonuses and the arc lighting system he designs isn't put into use, finds partners to build an arc lighting system in New Jersey but they then drop the manufacturing side and leave Tesla with no profits from his inventions

Tesla then invented a very simple thermoelectric motor
This brought him partners who better understood new technology
and business strategy--an alternative set up patents made it possible to set up a competing company
they even supported Tesla as he tried generating ideas that did not work

Patent and business strategy at the time:

• notice the importance of networking--Tesla needs people to put up the money for him to develop his invention, he wants this to be a partnership
• there are companies competing to sell electric power systems to cities
• Edison's patents meant that other companies couldn't build the same kind of systems, but they could invent alternatives and patent and sell those
• there are more games that can be played with patents:
• you can patent something you are never going to use to stop your competitor from using it
• you can invent and patent something to trade with another company for a patent you need
• you can use a patent as a bargaining chip to get a good price on an existing technology
• you can sue your competitor for infringing on your patent (copying it), resulting in a long expensive lawsuit slowing down the new idea
  

Tesla turned back to the motor and figured out how to do it with two polyphase currents (four wires) instead of 3, but wasn't interested in the simpler split phase (two wire)

meanwhile alternating current is catching on, led by Westinghouse, but it isn't the right kind of alternating current