I'm not sure how I would explain (as only one example among many) Facebook's market cap to our 1915 visitor. I think s/he would find it enigmatic, not having been along for the evolution of events.
The market cap concept is known pretty well to an educated visitor from 1915, exchanges had been in existence for more than two hundred years then. The number may seem big at first, but after explaining inflation impact and may be expressing this number as percent of GDP, this, too, does not seem to be far-fetched.
