Air-Breaker Cut-Out Switch?

To set the scene, look here:
http://www.collectorsweekly.com/stories/178606-exploring-urban-ruins-one-of-my-many-fo

The temperature was 98 degrees. Thankfully, humidity wasn't as bad as usual. Still, walking around a cement-and-dirt lot without trees or much (any) breeze, and having cycled out there, is not pleasant.
Nonetheless, I had found an intact porcelain insulator there (1930s-1940s) and had come back to continue searching even as the sun tore into my being which was also without a hat (Idiot!)
Poking around in some plants growing from ruined cement, I found shards to a number of porcelain insulators which I had been piling up for proper disposal (Sharp like knives!)
Suddenly, I see this and drag it out, seeing an insulator still intact on it (porcelain sleeve.)
Unable to remove that, I decided to just bring the entire thing home in my bike's baskets along with a few other items of interest.

The lot is now totally gone. Demolition is complete albeit its owner told me it took over a year to do.

It most matches a late-1930s patent. I'm guessing circa-1940s but dunno.
It technically still works, barring the shattered insulator. Everything moves like it should, it seems (I partially dismantled it.)

Read the other insulator here:
http://www.collectorsweekly.com/stories/176735-dig-of-porcelain-insulators-two-sites