Suppose letter A, is at the point, _b_, of the _disc_; and letter A of the _dial_ is opposite the opening; the instrument is now ready to transmit, and let the letter, I, be the first of the message. The operator gently turns the disc round in the direction of the arrow, so that each time the circuit is broken a new letter appears at the dial, and each time it is closed by the operation of the pallets, in checking and releasing the pin wheel. This is its operation until the letter, I, has reached the point, _b_, when a short pause is made. The next letter, H, requires but one movement of the disc, then follows, A; then, V; and then, E. In relation to this instrument, Professor Daniell says: “We can only further briefly allude to two of the most important modifications of this invention, which Prof. Wheatstone has made for specific purposes. By substituting for the paper disc, on the circumference of which the letters are printed, a thin disc of brass, cut from the circumference to the centre, so as to form 24 springs, on the extremities of which, types, or punches, are placed, and adding a mechanism the detent of which, acted on by an electro magnet, causes a hammer to strike the punch against a cylinder, round which are rolled, alternately, several sheets of white paper, and of the blackened paper used in the manifold writing apparatus, he has been enabled to obtain, without presenting any resistance to the type wheel, several distinct printed copies at the same time of the message transmitted.”[39] [39] Daniell’s Introduction to Chemical Philosophy, page 580, 2d Edition, London, 1843 Mr. Wheatstone has recently so modified his telegraph as to use two needles, or galvanometers, and two extended wires, with the ground as half the circuit for the two wires. He has thus adopted PROF. MORSE’S _plan_ of using the ground as a common conductor for two or more wires. He, however, still requires two wires for _one_ independent line of communication; one station only being able to communicate at a same time. He has no mode of recording his message, but depends upon the watchful eye of the attendant. His code of signals are based upon Schilling’s plan, heretofore described, page 155, and also Gauss and Weber’s, page 156, from whom he seems to have obtained his idea. The two needles, or galvanometers, stand side by side, one of which is called the _left_ needle and the other the _right_ needle. These two needles are placed directly in front of the person who transmits. There are, also, in front, two handles, one for each hand, with which the operator transmits a message, closing and breaking the circuit of the two wires. His signals are made thus: The upper half of the left hand needle moving to the left twice, gives, _a_; three times, _b_; once to the right and once to the left, _c_; once to the left and once to the right, _d_; and, in like manner, for the other letters of the alphabet, as shown in the table which follows.