This is an example of the kind of projector I worked on:
<http://www.unicornbookshop.com/trappehistory/artifacts-2/super-50-5.html>
The glass plate reading "Peerless" on the top would be illuminated
from the side via the carbon arc.
The window in the side curved door was welder's glass so you could
look at the arc and adjust the rods without blinding yourself.
The big round knob on the left center and bottom right were used to
adjust the distance between the two carbon rods that formed the arc.
Even though our theatre was running into the late 80s, they continued
using these projectors. I don't remember dating them specifically but
I would not be surprised if they dated from the 30s; the theatre
itself dated from the early teens.
It was torn down in the 90s, IIRC.
--
"The Direct3D Graphics Pipeline" free book
<http://tinyurl.com/d3d-pipeline>
The Computer Graphics Museum <http://ComputerGraphicsMuseum.org>
The Terminals Wiki <http://terminals.classiccmp.org>
Legalize Adulthood! (my blog) <http://LegalizeAdulthood.wordpress.com>