3177. ... The proof already given is, I think, sufficient for those who may repeat the experiments; but in order to accumulate evidence, as is indeed but proper in the first announcement of such a proposition, I proceeded to experiment with the magnetic power of the earth ... for if a room is cleared of all common magnets, then the terrestrial lines of magnetic force which pass through it, have one common direction ... Now the force being the same everywhere, the proportion of it to the current evolved in the moving wire is then perhaps more simply and directly determined, than in the case where, a small magnet being employed, the force rapidly changes in amount with the distance.
Google-1
Google-2

Published before 1923