Here's a pic I had on file for those of you that requested one. Yep, just a lowly Hemingray 42...with a 1920 Lincoln wheat penny embedded in the dome. My theory is the penny was somehow attached to the end of the mandrel and forced into the glass from the pinhole side, or dropped into the pinhole immediately after removal of the mandrel, then pressed into the molten glass with a narrow rod of some sort. Whatever the case, there was certainly some horseplay going on in the Hemingray factory the day this insulator was made.
It's truly amazing that it made it through the annealing process without shattering, but then copper being a softer metal may be the key? As far as I know, this is one of only two known insulators with an actual coin encased in the glass (no, coins placed in open bubbles don't count!). Several impressions of coins in dome tops exist. Value? Tough to say. Others have quoted a value in excess of $2,000. Whatever the case, it can be safe to say that not all Hemi 42's are worthless--this one is at least worth a penny!