This observation is closely related to the above-mentioned resistivity of the carbon-link, and corroborates it in a special case.
The resistance coils themselves are generally wound on brass or copper bobbins, with silk-covered manganin wire, which should first be aged by heating for about ten hours to a temperature of 140° C., to remove the slight tendency to change in resistivity which would otherwise present itself.
alloy of 40% nickel and 60% copper, with a high volume resistivity and almost negligible temperature coefficient.
Around Burraton resistivity anomalies were generally coincident with soil Ba anomalies, but there was no coincident gravity anomaly.
ferromagnetic metal into a semiconductor, the resistivity mismatch problem has to be overcome.