This is a 4th order Fresnel lens, not the original apparently but one taken from another light that was decommissioned. The Fresnel lenses apparently were very, very bright and could be seen farther than any other kinds. Numerous docents at the lights we visited said the formula for making the glass had been lost. Nowadays the lights are being replaced by LEDs.
And here is a photo of Hal and I in the tower, only 72 steps up. Aren't we the happy couple!
The stairs in the tower. That's a piece of Hal on his way back down.