An article from someone who knows little about the history of electric motors. I recommend "Men and Volts - A History of the General Electric Company" on this.<p>Early motors had serious limitations. DC motors wouldn't maintain constant speed as the load varied, had major brush wear problems, and tended to require frequent brush adjustment. Sprague, and the unknown person who invented carbon brushes, fixed that. AC motors wouldn't start under load. Tesla, Scott, and Steinmetz fixed that. Insulating materials were not very good. They were either flammable and subject to aging (varnished cambric, wood, paper) or not oil-tolerant and subject to aging (natural rubber). This limited the power density to less than 10% of what ordinary modern motors achieve.<p>The materials problem was particularly difficult. We're used to having quite good materials available for almost all purposes - insulators which can handle high temperatures and aren't brittle, wire that isn't brittle, low-cost ball bearings that run for years without oiling, all with consistent, repeatable properties from batch to batch. That was not the case up to WWII at all.<p>They did have asbestos, though. General Electric Deltabeston Wire. [1] "Will not age or crack." This was a high-end product around 1920.<p>[1] <a href="http://www.ebay.com/itm/1936-GENERAL-ELECTRIC-DELTABESTON-MAGNET-WIRE-VINTAGE-ART-AD-/272694282246?nma=true&si=2I0OYVyjQUHB%252F25t6tWPyk1oKCM%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557" rel="nofollow">http://www.ebay.com/itm/1936-GENERAL-ELECTRIC-DELTABESTON-MA...</a>