The receiving apparatus or °ticker° proper, RS, consists of apolarized relay PR (see sec tion Polar Duplex); an electromagnet, termed the °press° magnet PM; a typewheel TW, and an escape-wheel EW. A drum D by its weight F tends to rotate the shaft S on which TW and RW are mounted. The escape E is connected rigidly with an armature A of PR, and is pivoted at P. Relays PM and PR are in the same circuit, as shown. The line pulsations are of sufficient strength to oscillate rapidly the armature of the polarized relay, in con sequence of which the escapement E allows the escape wheel and type-wheel to revolve rapidly. Owing to the greater inertia of the press magnet lever it does not respond to these rapid pulsations of current. When, however, the cylinder T is brought to rest, the steady current operates PM and its lever is sharply attracted and prints a letter.
Assuming that the wheel W sends out 32 electrical pulsations in one revolution these pulsations will cause one revolution of the type-wheel. Thus, if the transmitter be set in motion with brush B resting on the seg ment that is in line with, say, the pin under key A; while the letter A on the type-wheel is opposite the platen P on the end of the lever of the press-magnet, it follows that for every revolution, or part of a revolution, of the cylinder just enough pulsations will be transmitted to cause the type-wheel to pre sent a letter opposite the platen corresponding to the key depressed. If the transmitter and type-wheel do not start with corresponding letters in the required position misprints fol low. This is obviated by devices which bring the apparatus to a °unison° point after a few revolutions of the cylinder. The speed of rotation of this apparatus is about 120 revolu tions per minute.
The apparatus shown prints letters only. When figures are to be printed, a figure wheel is placed on the shaft, side by side with the letter wheel, and a °shifting' device is em ployed which shifts the letter or figure wheel under the printing platen when a letter or figure is to be printed. Usually two wires are employed in the latter case, one to operate the °shift° apparatus.
In printing telegraph systems of the kind just mentioned, considerable loss of time en sues from the fact that frequently it is neces sary to rotate the type-wheel the greater part of a revolution in order to print one letter. Thus, if the letter A follows B in a given word, it will require 31 pulsations of current to print A, assuming that there are 32 letters and punctua tion marks on the type-wheel. If R follows C, 15 pulsations will be necessary. This conduces to a low rate of speed, perhaps an average of 30 to 40 words per minute; the message being printed on a paper strip.
Hughes' Printing Telegraph.—An under standing of the operation of this system may be Fathered in a general way from the im mediately preceding remarks. It is not, how ever, a step-by-step system, but depends for its operation on the synchronous rotation of two wheels, one at each end. When a key of the keyboard is depressed at the sending station it catches a pin on a rotating wheel, or chariot, but does not stop the wheel. The pin so caught,
however, at that instant causes the transmission of an electric current over the line. This pulsation in turn instantly operates an elec tromagnet at the receiving end which trips a device that throws the paper strip against the letter on a type-wheel which at that moment is in the printing position, and, assuming the transmitting and receiving apparatus to be in synchronism, a letter corresponding to the key depressed will be printed at the receiving station. The synchronous rotation of the wheels is obtained primarily by means of a pendulum at each station which is adjusted and arranged to ensure a proximate rate of rotation to the respective wheels, but as the pendulum,' alone cannot be depended upon to maintain proper synchronism, a cam arrangement is pro vided which, every time a letter is printed, moves into a receptacle on the edge of the printing wheel and corrects the synchronism of the wheel, putting the wheel slightly forward or backward, as may be necessary. Pulsations of current are thus only transmitted over the line when a letter is to be printed.
Buckingham Page Printer.— To avoid the loss of time due to the rotation of a single type-wheel with many characters the Buck ingham printer (in one of its forms) em ploys four very small octagonal type-wheels mounted side by side on one shaft. On the periphery of each wheel eight letters and other characters are placed, 32 in all. The shaft on which these type-wheels are mounted is so arranged that by an ingenious dispo sition of five electro-mechanically operated levers, it may be given both a lateral and a rotary motion such that any one of the 32 characters on the type-wheels may be placed before a given point for printing, by five pulsations of current. The selection and printing of any letter or punctuation mark are brought about by a cycle of six pulsations of current in all—that is, three alternations of polarity. These pulsations are of varying length, akin in this respect to the Morse alphabet. For example, the letter A will be selected by a dash, short space, dot, short space, dot; B by a dot, long space, dash, long space, dot, dots and dashes being made by positive currents, spaces by negntive cur rents, as in the Wheatstone automatic tele graph (q.v.). The combinations of dots, dashes and spaces representing the different letters comprise what is known as the Buck ingham alphabet. For the actual printing of a character the sixth pulse, corresponding to the space between letters and words in the Morse and Wheatstone systems, is utilized. This is .always a negative pulsation. In the preparation of messages .for transmission, and in the actual transnussion of messages this system is almost identical with the Wheat stone automatic telegraph, and if the Wheat stone receiver were employed the messages would be recorded as dots, dashes and spaces.