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Page:Popular Science Monthly Volume 70.djvu/237

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that in the pressure of cleaning batteries, or sweeping the room or doing some other kind of work, boy-like he forgot to disconnect the circuits.

With Mr. Coy's first board two telephonic connections only were possible at the same time. That is, two conversations only could be carried on at the same time. If a third subscriber desired connection, it was necessary to await the release of a lever by the disconnection of one of the other lines. Then the bright thought occurred to the boy operator that by wetting the tips of his fingers and placing them on the respective pegs, his arms would become the levers of the respective circles, and thus the two subscribers could talk through his body. This very ingenious makeshift served to tide over the brief period during which an addition of two more circles was made to the original board, thus increasing its capacity fifty per cent. But one day, while the boy-operator was letting his wet finger-tips perform the service, now taken care of by cords and plugs, the ring-off signal came in from a subscriber who had just had a powerful magneto installed, and the shock received ended that very convenient practice.

PSM V70 D237 Vertical telephone contact bars.pngFig. 11. Soon there were more than 150 subscribers on twelve subscriber-lines, and the ratio of calls per subscriber was constantly on the increase. So a new board was planned by Mr. Coy—and built by Mr. Snell, who is still in New Haven engaged in supplying equipment-specialties to telephone companies. This board (Fig. 10) had a line capacity of forty wires. Evidently switchboards of this type found favor for a time in the opinion of the parent company; for a circular issued in 1880, by the National Bell Telephone Company, contains the following suggestions, all of which were omitted from a circular of similar purport, issued a year later by the American Bell Telephone Company:

There are several styles of switchboards that may be used, all depending on the general principles for their operation. They consist essentially of horizontal and vertical bars crossing one another and arranged so that any horizontal bar can be connected to any vertical bar. It is chiefly in the methods of making the connection that the various switches differ. In what is known as the 'plug' switch, the connection is made by inserting a small metal plug at the point where the horizontal and vertical bars cross one another. There are several forms of the plug switch. . . . In what is known as the slide central office switch, the connections are made by means of a sliding