While reading the replies to this thread, and especially those regarding my question as to power line frequency, it dawned on me that some areas of New York City had DC power (mainly for elevator motors) until very recently. I don't know if NYC still uses DC anywhere, or whether their elevators (motors) now run exclusively on AC power. What were ther advantages (if any) of running elevator motors on direct current as opposed to AC? I'd think a motor winding wouldn't care if it were fed AC or DC power; the motor would run, regardless, unless there is some characteristic of line-operated motors that does make them sensitive to the type of current flowing through their windings. Come to think of it, I seem to remember reading something in an old electronics book or magazine years ago that stated if an AC motor were run on DC (intentionally or by accident), the windings would burn up immediately. I do know this can happen with any kind of equipment powered by a transformer, say a TV or radio. Plug one of these into a DC source and the transformer will burn out at once. I had an aunt who accidentally ruined a radio this way when she and her husband were on their honeymoon in the late '40s. They were in Canada (or some part of the US that still used DC power at that time), IIRC, and she or he accidentally plugged a radio designed for AC only into a DC outlet, or perhaps it was a 117-volt radio on a 220-volt circuit. Needless to say, however, the radio was immediately ruined.
As to 25/50 cycle power, when I read Reece's reply that some areas of New York state, especially Niagara Falls, had 115-volt 25-cycle AC power I was surprised. With the rest of the US mainly on 60-cycle AC certainly by the '50s, it seems strange to me that an area such as Niagara Falls would still be using 25 cycles. Maybe that area's proximity to Canada had something to do with it?
Some parts of Canada may have had 50-cycle AC for some time into the '60s, even after the US had converted most of its power grids to 60 cycles.