THE BIRTH OF THE VALVE

Radio Record, Volume I, Issue 4, 12 August 1927, Page 7

THE BIRTH OF THE VALVE

GREATEST RADIO INVENTION

You sit at your wireless set turning the dials, and through the night, from across the seas, comes music, speech, or morse, -but who ever ponders over the wonder of the whole thing? oe "What is the greatest radio invention?" Surely not a difficult question, yet some would hesitate to answer it. And not only is it the greatest radio invention, but also the greatest electrical invention. It is the vacuum valve-the three-element radio yalye without which our progress would be greatly handicapped. The ‘transcontinental telephone, our radio broadcast stations, public address sSystems, transmission of photos by ‘yadio, and other very important de-

velopments of modern life, depend | upon it. And to think that at the } base of all these wonderful inventions: lies the so-called Edison effect, a discovery made many years ago, and little thought of for-several years latert Thomas Alva Edison, the electrical wizard, in his pioneer work in _inves-* tigating the peculiarities and behaviour of the incandescent tamp, came tipon a phenomenon which was termed-the Edison effect. His work: 4ed him into the study of the physical ‘and chemical actions which take piace in higlily evacuated glass tulbs con-' taining an incandescent filament, ’ What Effect Is. By the term "effect"? physicists have long designated phenomena or -groups of phenomena which are new in themselves, and which fail to arrange themselves into any pivett theoretical classification or to admit of an explanation under existing theories. Thus we have in physics a large number of effects to which have been given the names of their discoverers, all of .thom have been distinguished -in the field of pure science, such as, for instance, the Peltier effect, having to do with the absorption ‘and evolution -of heat at the junction of two metals a current; the Thomson effect, having to ‘do with thermo-electric currents in a given metal; the Hall effect, having to do with the deviation of currents in a thin film under the ‘nfluence of.

a powerful magnetic field; the Pur- 4 kinje effect, having to do with the, variation .of sensibility of the eye or the ted and blue ends of the spectrum with high and low illumination; the Zeeman effect, having to do. with the displacetnent of spectral fines when | a radiating gas is submitted to a pow- | erful magnetic field, etc. Edison’s Great Discovery. Of ait these effects, none has been so ‘prolific -in’ practical consequences as the Edison effect, What is the Edison effect? It is best answered in Edison’s own words, which appear. in a patent filed by him in October, 1883 :-- . ; "T have discovered that if a conducting substance is interposed anywhere in the vacuous space within the { globe of an incandescent ‘amp, and said conducting substance ‘is connected outside of the lamp with one terminal, preferably the positive one the incandescent conductor, a portion of the current will, when ‘the lamp is in operation, pass through the shunt circuit thus formed." In ‘other «words, Edison was the: first to notice that a current flowed through the space in the evacuated tube, but since ‘at that early date electrons were unheard of, no Satisfactory ex-. planation was available. . Clearer Idea Now. To-day, in the light of Richardson’s

formulas governing the laws of emis-' sion and Langmuir’s supplementary «work ’ showing the -so-called space charge effect, we are able to give an accepted hypothesis showing that the Edison effect is simply this: that. negatively charged particles of electricity, called electrons, are shot off from an incandescent conductor, such as a heated filament, and that these elec‘trons are attracted either by the posi--tive leg of the filament or by a second conductor, ‘called a plate. The thermionic current which flows is unilateralx We then have ‘the substance of a ‘rectifying valve which will conduct currents in one direction only. And,-due only to the fact that Edison was too busy with the develop-. ment ‘of the electric lamp, his discovery was not practically applied until Fleming (the English scientist) took advantage of it and applied it to the reception of wireless signals, eleven years afterwards. Fleming, in ‘Principles ef Electric Wave Telegraphy," states:-"A third method of utilising the properties of rarefied gases for the purpose of a cymoscope was discovered by the author in 1904, based upon a fact discovered by him in 1890 in the course of some investigations upon incandes- cent electrical lamps." , This statement would lead one to believe that Fleming was responsible: for the discovery of the fact'that electronic emission takes place when a

filament is heated, and that the elec tronic stream is conductive in one di-~ rection only. Credit Claimed for Edison, The Americans claim that the full’ credit belongs to Edison, since what LY 2 Fleming merely did was to apply the known principle to the rectification wireless waves. ‘The fact, they urge, that no mention has been made by Fleming on the Edison effect has ‘beet erroneously construed by some to indicate that Fleming first came upon the principle. From the Fleming valve, which was not particularly effective as a wireless ° detector, the next advance made was : a S-electrode tube as conceived by De. Forest.’ This remarkable step forward was the introduction of a third | element-the grid-which could regulate ‘the passage of the electrons be-~.’ tween filament and plate. The audio or 8-electrode tube, in its : property of operating as a detector or’ rectifier of signals, as an amplifier, . and generator of alternating currents _, of any frequency, is a most wondet-. ful and versatile piece of apparatus.. Since its inception by. De Forest it has. undergone some remarkable develop.» ment-work, and from the unpretentious "oscillion valve" to the 100 kilo~watt water-cooled power tube is a tre-: ~mendous stride.