Carbon Arc Movie projectors

Spent many a year with these, 35mm and 70mm. 

The two rods had to kept within a certain distance from each other to produce the correct lighting. The projectionist would watch the reflected light on a paper target and by turning dials adjust the rods in and out to keep the burn correct

Spent carbon Rods..

Film used to be highly flammable and projectionists had to be licensed through the State Fire Marshall's office.
The film was so explosive that the projectors had cables with lead melt fuses attached to steel panels above them. In the event of fire the lead would melt and separate the cable releasing the steel plates to drop over the projection booth windows to contain the fire. The booth was fire proof so fire wouldn't spread to the rest of the theatre. The Booth in the event of fire became the projectionist's crematorium.