Caper:
If you haven't already looked at it, cast an eye on Trainwire's thread in this discussion area entitled "32 volt DC lighting panel". There are some pix of a wonderful old panel, as well as an interesting description of it. [Linked Image]

Regarding the large ceramic rheostat pic you posted, I have run into a couple of these in the past. They were used to regulate the amount of DC voltage being fed to two carbon arc lamps in a theater projection room. If memory serves me, I believe only one end of the coil was connected to the DC source (a motor-generator set)and the tap connection fed to a large ballast resistor, then to the arc lamp. I think these rheostats were made by Ohmite, and each had a large control knob like the one you posted.

Circuit Man: I like old meters also. Have two or three in my collection. Down in this area (SE Texas), they are pretty hard to come by. Can you post some pix of your collection?

Mike (mamills)