CD 1967017 E&MP44.160
One of the most useful instruments of science for measuring minute electric currents is the Wheatstone Bridge, which does for electricity what a delicate beam balance does for weighing masses.
In the Wheatstone Bridge which the girl is operating above, two currents are made to buck one another and a delicate "zero" balanced reading is obtained. If, then, a very small extra current flows through one of the two opposing circuits the whole system is thrown out of balance.
It then has to be readjusted to bring it back into balance and the amount of this adjustment is a measure of the tiny current. Wheatstone bridge adapted to measurement of temperature.(Esther C. Vaughn, U.S. Bur. of Standards)
Original Caption by Science Service
©National Bureau of Standards