from The Century Dictionary and Cyclopedia
- n. A steel bar which is placed in an oven or furnace in which steel is undergoing the process of cementation, and which is withdrawn from time to time by the attendant so that he may judge of the progress of the operation.
Sorry, no etymologies found.
"Pipe down that guff, you unlicked cub, or I'll crown you with a proof-bar!" the chief pilot growled, as soon as Stevens had unplugged.
"You couldn't squeeze another frank into our accumulators with a proof-bar, and since they're sending us all the power we want to draw, we won't need to touch our batteries or tap our own beam until we're almost to Jupiter.