"Aerophony" as used in this article was a Lee DeForest inspired term -- Hogan had worked in his laboratory -- that never caught on, with "radiotelephone" becoming the preferred descriptor. Also characteristic of a DeForest approach to the subject is that it has only a vague idea of how an Audion works and avoids any mention of how similar it is to the two-element Fleming valve.
Modern Electrics, October, 1908, pages 232-233:
The Audion; A Third Form of the Gas Detector
BY JOHN L. HOGAN, JR.
Two methods by which a sensitive column of conducting gas may be used as an oscillation responder have been considered in the Flame and in the direct current Arc*.
It has been found that the gas column is a most delicate medium upon which to build the trigger action of a responsive device. But it has also been found that the conducting gas flame and the arc are unsteady--that their very sensitiveness operates against their practical efficiency because they respond emphatically not only to Hertzian waves, but to air currents. This of course makes them useless for commercial wireless.
The extreme delicacy of the gas detector of course renders it sensitive not only to complete starts and stoppages of received electric waves (as in wireless telegraphy), but also to slight variations in them. Therefore the apparatus may be believed highly suitable for aerophony, if it could be caused to respond to Hertz waves only, and kept from hissing and rattling in the telephones at every gust of wind.
It was found over twenty-five years ago in Germany, that if a metallic plate and a filament were sealed side by side in an evacuated globe, a current could be passed from the filament to the plate while the filament was lighted, but not otherwise. After a long series of tests it was discovered that the hot filament emitted a flow of ions which carried the current from filament to plate. This flow is exactly analogous to that in the gas flame and in the arc, but for a long time it was not considered that it could be used as a nearly ideal wave detector.
After several notable steps of development by different workers, the device now known as the Audion was produced. This has been modified and so changed in the course of its growth that there are now some six or more distinct varieties. In all these the operating principle is the shattering of a column of conducting gas by a received electrical impulse. But, unlike the flame and arc detectors, the gas column is protected from air currents by the globe of the Audion-lamp, so it is evident that the great difficulty mentioned above has been eliminated.
The most sensitive type so far designed is called the Grid Audion. This is usually a six-volt low candle-power incandescent lamp with a tantalum filament, having a small platinum plate (about 10x15 millimeters) fastened approximately three millimeters from the filament, and a "grid" bent from rather large (say number twenty-two) platinum wire placed nearly midway between the two. The filament is lighted by three small storage cells, whose output is varied by a rheostat having continuous smooth adjustment. From the positive terminal of this storage battery a wire is led to the adjustable high voltage battery of the telephone circuit, as shown in the diagram. The two leads from the tuning apparatus are respectively connected to the grid and to the negative side of the storage cells.
It has been definitely stated that the Audion is a potential operated device. But on the same authority it is said that the Audion is dependent for its response upon the total energy received, so the class to which the apparatus really belongs is somewhat hazy.
It is undoubtedly true that the Audion, when in its best condition, is highly sensitive and that it is therefore well suited to aerophony. But unfortunately the sensitive condition is extremely difficult to find and still more difficult to maintain. Some Audion-tubes show an extraordinary sensitiveness at first, but quickly grow dull when in use. Other lamps are nearly worthless from the beginning, and none remain sensitive very long.
The Audion is capable of being developed into a really efficient detector, but in its present forms is quite unreliable and entirely too complex to be properly handled by the usual wireless operator. The principles involved are of the utmost importance, but their application is crude and irregular.
The Audion offers another fascinating field for investigation and improvement, and it is to be hoped that it will be taken up and the work so well begun carried to a satisfactory conclusion. For aerophony a detector is needed which will reproduce with fidelity the higher harmonics of the voice. The Audion, when carefully handled, is such a detector, but the best adjustment is so very critical that the manufacturers of aerophonic apparatus have found that almost no demand for the tubes exists, and are therefore supplying crystalline thermo-electric detectors with their outfits. This fact, together with the unsatisfactory results of tests made by the Government and by one of the foremost wireless companies in America, would seem to indicate that as yet the device is not to be absolutely depended upon and is therefore not to be used in the serious undertakings of aerophonic communication.
*See article by Mr. Hogan in the June and September issues.--Editor.