APPENDIX I. THE STOCK PRINTER

IN these modern days, when the Stock Ticker is in universal use, one seldom, if ever, hears the name of Edison coupled with the little instrument whose chatterings have such tremendous import to the whole world. It is of much interest, however, to remember the fact that it was by reason of his notable work in connection with this device that he first became known as an inventor. Indeed, it was through the intrinsic merits of his improvements in stock tickers that he made his real entree into commercial life.

The idea of the ticker did not originate with Edison, as we have already seen in Chapter VII of the preceding narrative, but at the time of his employment with the Western Union, in Boston, in 1868, the crudities of the earlier forms made an impression on his practical mind, and he got out an improved instrument of his own, which he introduced in Boston through the aid of a professional promoter. Edison, then only twenty-one, had less business experience than the promoter, through whose manipulation he soon lost his financial interest in this early ticker enterprise. The narrative tells of his coming to New York in 1869, and immediately plunging into the business of gold and stock reporting. It was at this period that his real work on stock printers commenced, first individually, and later as a co-worker with F. L. Pope. This inventive period extended over a number of years, during which time he took out forty-six patents on stock-printing instruments and devices, two of such patents being issued to Edison and Pope as joint inventors. These various inventions were mostly in the line of development of the art as it progressed during those early years, but out of it all came the Edison universal printer, which entered into very extensive use, and which is still used throughout the United States and in some foreign countries to a considerable extent at this very day.

Edison's inventive work on stock printers has left its mark upon the art as it exists at the present time. In his earlier work he directed his attention to the employment of a single-circuit system, in which only one wire was required, the two operations of setting the type-wheels and of printing being controlled by separate electromagnets which were actuated through polarized relays, as occasion required, one polarity energizing the electromagnet controlling the type- wheels, and the opposite polarity energizing the electromagnet controlling the printing. Later on, however, he changed over to a two-wire circuit, such as shown in Fig. 2 of this article in connection with the universal stock printer. In the earliest days of the stock printer, Edison realized the vital commercial importance of having all instruments recording precisely alike at the same moment, and it was he who first devised (in 1869) the "unison stop," by means of which all connected instruments could at any moment be brought to zero from the central transmitting station, and thus be made to work in correspondence with the central instrument and with one another. He also originated the idea of using only one inking-pad and shifting it from side to side to ink the type-wheels. It was also in Edison's stock printer that the principle of shifting type-wheels was first employed. Hence it will be seen that, as in many other arts, he made a lasting impression in this one by the intrinsic merits of the improvements resulting from his work therein.

We shall not attempt to digest the forty-six patents above named, nor to follow Edison through the progressive steps which led to the completion of his universal printer, but shall simply present a sketch of the instrument itself, and follow with a very brief and general explanation of its theory. The Edison universal printer, as it virtually appears in practice, is illustrated in Fig. 1 below, from which it will be seen that the most prominent parts are the two type-wheels, the inking-pad, and the paper tape feeding from the reel, all appropriately placed in a substantial framework.

The electromagnets and other actuating mechanism cannot be seen plainly in this figure, but are produced diagrammatically in Fig. 2, and somewhat enlarged for convenience of explanation.

It will be seen that there are two electromagnets, one of which, TM, is known as the "type-magnet," and the other, PM, as the "press-magnet," the former having to do with the operation of the type- wheels, and the latter with the pressing of the paper tape against them. As will be seen from the diagram, the armature, A, of the type-magnet has an extension arm, on the end of which is an escapement engaging with a toothed wheel placed at the extremity of the shaft carrying the type-wheels. This extension arm is pivoted at B. Hence, as the armature is alternately attracted when current passes around its electromagnet, and drawn up by the spring on cessation of current, it moves up and down, thus actuating the escapement and causing a rotation of the toothed wheel in the direction of the arrow. This, in turn, brings any desired letters or figures on the type-wheels to a central point, where they may be impressed upon the paper tape. One type-wheel carries letters, and the other one figures. These two wheels are mounted rigidly on a sleeve carried by the wheel-shaft. As it is desired to print from only one type-wheel at a time, it becomes necessary to shift them back and forth from time to time, in order to bring the desired characters in line with the paper tape. This is accomplished through the movements of a three-arm rocking-lever attached to the wheel-sleeve at the end of the shaft. This lever is actuated through the agency of two small pins carried by an arm projecting from the press-lever, PL. As the latter moves up and down the pins play upon the under side of the lower arm of the rocking- lever, thus canting it and pushing the type-wheels to the right or left, as the case may be. The operation of shifting the type-wheels will be given further on.

The press-lever is actuated by the press-magnet. From the diagram it will be seen that the armature of the latter has a long, pivoted extension arm, or platen, trough-like in shape, in which the paper tape runs. It has already been noted that the object of the press-lever is to press this tape against that character of the type-wheel centrally located above it at the moment. It will at once be perceived that this action takes place when current flows through the electromagnet and its armature is attracted downward, the platen again dropping away from the type-wheel as the armature is released upon cessation of current. The paper "feed" is shown at the end of the press-lever, and consists of a push "dog," or pawl, which operates to urge the paper forward as the press-lever descends.

The worm-gear which appears in the diagram on the shaft, near the toothed wheel, forms part of the unison stop above referred to, but this device is not shown in full, in order to avoid unnecessary complications of the drawing.

At the right-hand side of the diagram (Fig. 2) is shown a portion of the transmitting apparatus at a central office. Generally speaking, this consists of a motor-driven cylinder having metallic pins placed at intervals, and arranged spirally, around its periphery. These pins correspond in number to the characters on the type-wheels. A keyboard (not shown) is arranged above the cylinder, having keys lettered and numbered corresponding to the letters and figures on the type-wheels. Upon depressing any one of these keys the motion of the cylinder is arrested when one of its pins is caught and held by the depressed key. When the key is released the cylinder continues in motion. Hence, it is evident that the revolution of the cylinder may be interrupted as often as desired by manipulation of the various keys in transmitting the letters and figures which are to be recorded by the printing instrument. The method of transmission will presently appear.

In the sketch (Fig. 2) there will be seen, mounted upon the cylinder shaft, two wheels made up of metallic segments insulated from each other, and upon the hubs of these wheels are two brushes which connect with the main battery. Resting upon the periphery of these two segmental wheels there are two brushes to which are connected the wires which carry the battery current to the type-magnet and press- magnet, respectively, as the brushes make circuit by coming in contact with the metallic segments. It will be remembered that upon the cylinder there are as many pins as there are characters on the type-wheels of the ticker, and one of the segmental wheels, W, has a like number of metallic segments, while upon the other wheel, W', there are only one-half that number. The wheel W controls the supply of current to the press-magnet, and the wheel W' to the type- magnet. The type-magnet advances the letter and figure wheels one step when the magnet is energized, and a succeeding step when the circuit is broken. Hence, the metallic contact surfaces on wheel W' are, as stated, only half as many as on the wheel W, which controls the press-magnet.

It should be borne in mind, however, that the contact surfaces and insulated surfaces on wheel W' are together equal in number to the characters on the type-wheels, but the retractile spring of TM does half the work of operating the escapement. On the other hand, the wheel W has the full number of contact surfaces, because it must provide for the operative closure of the press-magnet circuit whether the brush B' is in engagement with a metallic segment or an insulated segment of the wheel W'. As the cylinder revolves, the wheels are carried around with its shaft and current impulses flow through the wires to the magnets as the brushes make contact with the metallic segments of these wheels.

One example will be sufficient to convey to the reader an idea of the operation of the apparatus. Assuming, for instance, that it is desired to send out the letters AM to the printer, let us suppose that the pin corresponding to the letter A is at one end of the cylinder and near the upper part of its periphery, and that the letter M is about the centre of the cylinder and near the lower part of its periphery. The operator at the keyboard would depress the letter A, whereupon the cylinder would in its revolution bring the first-named pin against the key. During the rotation of the cylinder a current would pass through wheel W' and actuate TM, drawing down the armature and operating the escapement, which would bring the type-wheel to a point where the letter A would be central as regards the paper tape When the cylinder came to rest, current would flow through the brush of wheel W to PM, and its armature would be attracted, causing the platen to be lifted and thus bringing the paper tape in contact with the type-wheel and printing the letter A. The operator next sends the letter M by depressing the appropriate key. On account of the position of the corresponding pin, the cylinder would make nearly half a revolution before bringing the pin to the key. During this half revolution the segmental wheels have also been turning, and the brushes have transmitted a number of current impulses to TM, which have caused it to operate the escapement a corresponding number of times, thus turning the type-wheels around to the letter M. When the cylinder stops, current once more goes to the press-magnet, and the operation of lifting and printing is repeated. As a matter of fact, current flows over both circuits as the cylinder is rotated, but the press-magnet is purposely made to be comparatively "sluggish" and the narrowness of the segments on wheel W tends to diminish the flow of current in the press circuit until the cylinder comes to rest, when the current continuously flows over that circuit without interruption and fully energizes the press-magnet. The shifting of the type-wheels is brought about as follows: On the keyboard of the transmitter there are two characters known as "dots"-- namely, the letter dot and the figure dot. If the operator presses one of these dot keys, it is engaged by an appropriate pin on the revolving cylinder. Meanwhile the type-wheels are rotating, carrying with them the rocking-lever, and current is pulsating over both circuits. When the type-wheels have arrived at the proper point the rocking-lever has been carried to a position where its lower arm is directly over one of the pins on the arm extending from the platen of the press-lever. The cylinder stops, and current operates the sluggish press-magnet, causing its armature to be attracted, thus lifting the platen and its projecting arm. As the arm lifts upward, the pin moves along the under side of the lower arm of the rocking-lever, thus causing it to cant and shift the type-wheels to the right or left, as desired. The principles of operation of this apparatus have been confined to a very brief and general description, but it is believed to be sufficient for the scope of this article.

NOTE. The illustrations in this article are reproduced from American Telegra- phy and Encyclopedia of the Telegraph, by William Maver, Jr., by permission of Maver Publishing Company, New York.