This item looks very very old, and some might call it a carbon pile. A laboratory piece for sure. I measured this item and it read down to 1 ohm which is the lowest I can go on my inexpensive DVM. The cast iron handwheel and screw turn to increase the resistance (uncompress the carbons) or decrease the resistance (compress the carbons). The outside of the carbons are dusty, but the flats are nice and clean. The carbon blocks rest on a V groove made of what looks like slate (I don't know) and a wood plate with some heat insulating cloth-like material. Can you say "asbestos"?