ClipArt ETC
"Represents in diagram the arrangement of the battery, resistance, and galvanometer. There are two keys, K and K, , placed in the circuit whose uses will be subsequently explained for the present, the diagram will be considered as if these keys did not exist, and as if the current flowed permanently through. the circuits as is indicated by the arrow-heads." (Britannica, 1891)

Arrangement of Battery, Resistance, and Galvanometer

"Represents in diagram the arrangement of the battery, resistance, and galvanometer. There are two keys,…

"The galvanometer consists of two distinct coils of wire, each having the same resistance, and having equal magnetic effects upon the needle. These coils C and C' are wound in opposite directions, as shown, and one end of each is joined to the same terminal on the frame of the galvanometer; the other ends are joined to separate terminals also situated on the frame." (Britannica, 1891)

Differential Galvanometer

"The galvanometer consists of two distinct coils of wire, each having the same resistance, and having…