Jim Redelfs wrote:

The "ring" conductor should have -48-52VDC-to-ground on it. You'll notice I
said NEGATIVE 48VDC. Everything in the C.O. battery room is labeled as
NEGATIVE. You tell me. sigh

Corrosion and oxidation are less likely to occur on lines that are
negative to ground than positive. Hence, outside telephone plant is
positive ground.