File:EB1911 Telegraph - Wheatstone Automatic Transmitter.jpg

English: The paper ribbon generated by the telegraphy mechanism of EB1911 Telegraph - Wheatstone Punching Apparatus.jpg is used for the transmission of a message via the transmitter illustrated here. An ebonite beam B is rocked up and down rapidly by a train of mechanism, and moves the cranks A and A′ by means of two metal pins P, P′. A and A′ carry two light vertical rods S, M, the one as much in front of the other as there is space between two successive holes in the perforated ribbon. To the other ends of A, A′, rods H, H′ are loosely hinged, their ends passing loosely through holes in the end of the bar L. By means of two collars K, K′, the lever L is made to oscillate in unison with the beam B. The operation is as follows: the paper ribbon or perforated slip is moved forward by its centre row of holes at the proper speed above the upper ends of the rods S, M; should there be no holes in the ribbon then the cranks A, A′ will remain stationary, although the beam B continues to rock, since the rods S, M are pressing against the ribbon and cannot rise. Should, however, a row of holes, like group 1 of EB1911 Telegraph - Wheatstone Punching Apparatus.jpg, be in the ribbon, the rod M will first be allowed to pass through the paper, and the corresponding movement of crank A′ will, through the agency of collet K, throw over lever L, and the battery zinc will be put to the line; at the next half stroke of the beam, S will pass through, and crank A by its movement will, through the agency of collet K′, throw over lever L in the reverse direction, so that the battery copper will be put to the line. Thus for a dot, first a negative and then a positive current is sent to the line, the effect of the current continuing during the time required for the paper to travel the space between two holes. Again, suppose groups 3 and 4 to be punched. The first part will be, as before, zinc to the line; at the next half stroke of the beam M will not pass through, as there is no hole in the paper; but at the third half stroke it passes through and copper is put to the line. Thus for a dash the interval between the positive and the negative current is equal to the time the paper takes to travel over twice the space between two successive holes. Hence for sending both a dot and a dash, reverse currents of short duration are sent through the line, but the interval between the reversal is three times as great for the dash as for the dot.