4 slides from Grampa's collection from the 1939/40 World's Fair. He must have especially liked these four out of the 20+ slides I've found so far from this event (which he attended three times, twice in 1939 and once in 1940) because he had sealed them in glass. I was amazed to find that I was able to scan them without opening the casing.
This, as far as I can tell, is a demonstration, probably at the GE pavilion, of "lightning" hitting a model of the Trylon and Perisphere. Grampa was a science geek and not a few images in the collection reflect this keen interest.