Figure 49 represents those connections which are formed when the left hand side of the lever is depressed, immersing in the mercury those wires supported by it. The ball and lever are omitted for the better inspection of the wires. Now the circuit is closed, and the current is passing from P, of the battery, to the mercury cup, 1; then along the cross wire to 4; to 8; to the coils of the multiplier, deflecting the needle to the _right_; then to 7; to 3; then along the cross wire, (which is not in contact with wire 1 and 4,) to 2; to the N pole of the battery. The arrows also show the direction of the current. It will be observed that the cups 5 and 7, and 6 and 8 are not now in connection, and consequently the current cannot pass along the wires 1 and 5, and 2 and 6. [Illustration: FIG. 50.] Now, if the ball, D, is carried to the right, a new set of wires, figure 50, are immersed, and those represented in figure 49, as in connection, are taken out of their cups. The fluid now passes from P, of the battery, to the mercury cup, 1; to 5; to 7; to the coils of the multiplier, deflecting the needle to the _left_; then it passes to cup 8; to 6; to 2; and then to the N pole of the battery; the arrows representing the direction of the current. It will now be found, that the cups, 2 and 3, and 1 and 4 are not in connection, and consequently the current cannot pass along the wires, 3 and 7, and 4 and 8. Thus, it will appear, that by carrying the ball, D, to the left, the needle is deflected to the _right_; then, by carrying the ball to the right, the needle is deflected to the _left_; and that when the ball is brought to the vertical position, the needle is _vertical_. These three changes enter into the plans of several electric telegraphs, which are to be hereafter described. _Professor Morse’s American Electro Magnetic Telegraph, invented, 1832._ To our readers the principles and arrangement of Morse’s telegraph have been fully explained in the former part of this work. We shall here present _some_ of the evidence of the time of its invention. _Extract from a letter from S. F. B. Morse to the Hon. Levi Woodbury, Secretary of the Treasury, dated Sept. 27th, 1837._