Page:Popular Science Monthly Volume 88.djvu/99



USIC that ranges from the piercing wail of a taut violin string to the grumbling bass of a monster horn has been added to the remarkable achievemntsachievements [sic] of an electrical instrument so small and so insignificant in appearance that it could be passed by scores of times without arousing so much as a lingering glance. Despite its innocent appearance, however, its technical name is more than formidable. Scientists know it as the "oscillating vacuum tube," although this name has been changed and shortened to a simple compound word, "audion." "Audion" is derived from audio, to hear, and ion, the tiniest division of electricity; in other words, to make audible the action of ions. This, in a word, is exactly what the oscillating vacuum tube accomplishes.

Before proceeding directly to a discussion of the latest marvel of the audion,—electrical music—let us pass hurriedly over some of the achievements that have preceded it, which, in a round-about way, have led to the discovery.

Amateur and professional wireless operators know the audion well, although numbers of them are not aware that it has other uses than the reception of radio signals.

Connected with the proper wireless instruments, the audion will receive and strengthen the weak signals of a distant radio station to a degree several times as loud as any other detector. But its ability in this direction does not stop there. If several of the tubes are connected in the correct way and adjusted with great care, the wireless signals will be increased in loudness several hundred times. This arrangement is known as the Audion amplifier.



In both of these uses, the construction and operation of the audion are practically the same. In fact, for all of the uses to which the audion is put, its fundamental structure, apart from size, does not vary. In appearance it closely resembles an ordinary electric lamp bulb. There is a brass base with threads, so that it can be screwed into a socket, a round glass bulb and a filament burning brightly in a partial vacuum. But beyond this point, the audion and the electric light are strangers.

Built into the bulb close to the filament are two metal electrodes. One is a tiny replica of the grids that are used in coal stoves and it is called a grid; while the other is a small plate. The grid and the plate are connected to the other apparatus in such a way that a perfect balance, electrically speaking, is maintained between them. When an outer influence, such as an incoming wireless wave, is brought into the bulb, this balance is disturbed, and in a strengthened form, the disturbance is heard in the telephone head receivers as the dots and dashes of the wireless code.

Strange to say, this same balancing principle is made use of in another application directly opposite in na-