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No, it is the changing magnetic field.
Each time the field reverses, the rotor moves
one cog of the rotor.
I believe this is a spin start and not a self start.
The coil should not get really really hot. It should
generate about as much heat as the older
Christmas tree lights. The core shouldn't get more
than about 45C. ( 50C where you can't hold your finger
on it for more that a few seconds ).
The movement in your electric clock is one of the simplest types that became popular in the 1930's in the US. It's generically called as, Tinker explained, the "spin to start" kind.
The heat generated by AC electric clocks is a loss. The two or three watts of electrical power used by most AC electric clocks is mostly lost as heat. Less than a tenth of the electrical power is used to turn the hands. The losses are unavoidable on account of the selection of iron and other materials used in their design to make them practical household items.
They were good for their day because the self-starting kind were not accurate after an interruption of electric service. (a common happening in those days) On the other hand, the spin-to-start clocks stopped dead still after an interruption of electrical service showing the user that the time was not to be trusted.
The movement in your clock is one invented and patented by Max Knobel. It's simple and inexpensive to manufacture and very reliable. Knobel's electric clock movement was widely copied by many small-time manufacturers, particularly in the Chicago area. Rarely are they found with Knobel's patent notation.
Take care of your clock, lubricate the rotor bearings and if there's a large fiber gear, smear a little grease on the teeth once every fifteen years and the movement will serve for generations. (this advice valid only for this kind of clock)
55 years ago we had a mantel clock that would run backwards after a power cut. My father would have to turn the power off and back on again (I believe) to get it going forwards again. Was that a fault do you think, or a way of knowing it was no longer telling the correct time?
If the power loss was just a short one, the clock could
have started backwards. Some self starting clocks had a special
one-way clutch to keep them from starting backwards.
It is likely that yours may have been of this type that the
clutch was warn out.
Newer shade pole clocks would always start the right way.
So these were pre shaded pole then? I told my schoolteacher when I was 7 that the clock did this and he told me I was a liar. 52 years later I haven't forgotten that. I learned about shaded pole motors when I went to college and that didn't help, I assumed it must have been something to do with age. (the clock's, not mine)
Thanks for clearing that up, I suspect the teacher is long gone.