complete and the current would pass along the wire, ̈1, for example, to the metallic stop, then to the arm, and to the magnetic bar; then to the axis; then to the mercury; then to the wire, I, and thence to the wire, 8. In the same manner the current would pass if any other arm was brought against _its_ metallic stop. All the wires represented in this figure are permanently secured in their places upon a common platform. [35] A′, B′ and C′ are also, occasionally, common communicating wires. In order to understand the combined operation of the keys and needles, figure 70 is here introduced. The right hand figure, is the same as figure 69, and the left hand the same as figure 66. [Illustration: FIG. 70. _Transmitting Part of Receiving_ _Station. Station._] The wires, D″, A′, B′ and C′, are detached from their corresponding wires of the transmitting station, and it may be imagined that many miles of wire intervene and connect the two. In the left hand figure, those mercury cups above and below, 1 and 10, are joined by two wires passing through a moving lever, in the same manner as has been described in figure 67. We will, therefore, call the key, carrying these two connecting wires, H. In like manner the key for the cups above and below the numbers, 2 and 20, is called J; for 3 and 30, is K; for 4 and 40, is M; for 5 and 50 is O; for 6 and 60, is U. The key which connects the two mercury cups on the right and left of number 7, of the wire, D″, is called 7. There are 7 keys; two for each battery, 1′, 2′ and 3′, and each wire, A′, B′ and C′; and one for the common wire, D″. It will now appear, that if the key, U and 7, are depressed, the cups above and below, numbers 6 and 60; and the cups on each side of number 7, will be connected together so that the current leaving, P, or the positive pole of the battery, 3′, goes to the lower cup, 50; then by the stationary cross wire to upper cup, 6; then passes to lower cup, 6, by the wire supported by the lever, U, which is now pressed down, and its ends immersed in the two cups; then along the wire, D, to the left hand cup, 7; then to the right hand cup, 7, by the wire supported by the lever, 7, and which is immersed in the two cups; then through the extended wire to D″, of the _receiving_ station; then through 9, to the two multiplying coils of the wire, C′, deflecting the arm of the needle, R, to the right, against the stop, V; and the arm of the needle, R′, to the left against the metallic stop, S, as indicated by the arrow at S; then along the extended wire, back to the lower cup, 60, of the _transmitting_ station; then to upper cup, 60, through the wire supported by the lever, U; then to N, the negative pole of the battery, 3′.