[RightWhale]

That's interesting. I almost bought a fresnel lens 8" x 8" in the stationary store today just because it was a fresnel lens. I believe each prism in the original fresnel lens would have been curved a little rather than flat-faced, a segment of what would have been a huge and really heavy lens if the whole construction were one single piece of glass. The prisms would have to go in a particular place in the frame due to their shape and to get a good lens effect. What was the original light source? A carbon arc or gas lamp?

[Constitution Day]

I think you're right about the construction of the Fresnel lenses, but as to the original light source, no idea.