DeForest Radio Co. v. General Electric Co.

delivered the opinion of the Court.

Certiorari was granted, 282 U. S. 836 , to review a judgment of the Court of Appeals for the Third Circuit, holding the Langmuir Patent, No. 1,558,436, granted October 20,1925, for “ electrical discharge apparatus and process of preparing and using the same,” valid, and infringed by petitioners. The District Court for Delaware, in which respondent, the assignee of the patent, brought suit for infringement, held the patent invalid for want of invention, and because of prior use and prior invention, and gave judgment dismissing the complaint, 23 F. (2d) 698 , which the Appellate Court at first affirmed, and then, on reargument, reversed. 44 F. (2d) 931 .

Infringement is conceded if the claims of the patent are valid. It is known as a high vacuum tube patent, and

A radio tube of the aud'ion or three electrode type con-’ sists of a bulb, within which a vacuum has been created, enclosing a filament, which is a negative electrode, or cathode; a plate, which is a positive electrode, or anode; and a third electrode, known as a grid, located between the filament and the plate. The grid is connected with an input circuit, over which electrical radio activity, actuated at the sending station, is gathered from the ether and passes to the grid. When the tube is used as an amplifier, the plate is connected in circuit with a telephone receiver or loud speaker. In operation, the filament is heated to incandescence by passing an electric current through it. In its incandescent state, electrons, or negative charges of electricity, are developed at the filament and pass to the plate, attracted to it by its positive potential, and cause a flow of electricity through the plate-loud-speaker circuit. •• The sounds given out by the loud speaker are produced by variations in the current passing to it. Radio amplification depends on producing in the more powerful current of the loud speaker circuit, variations exactly corresponding to the variations in the weaker input or voice current which are actuated by the sending station.

In the vacuum tube of the three electrode type, this is accomplished by passing the input or voice current over the grid. Variations in that current produce variations in potential of the grid which, by reason of its location between the filament and plate, effects like variations in the

Of critical importance in the present controversy is the effect of the presence of gas within the tube. As in the practical art of bulb manufacture no scientifically perfect vacuum can be attained, air or other gas. is always present within the vacuum tube. This consists of a small amount of residual gas, after the vacuum is created by pumping out the tube in' the process of manufacture. There is also gas in the walls of the bulb and the electrodes, described as “ occluded,” which, if not expelled from them and removed in the course of manufacture, is later freed in varying amounts when the tube is in use, by the action of the heat of the filament and the electrons generated there.

The passage of electrons from filament to plate at certain voltages produces changes in. the gas, known as “ionization.” Ionization is the manifestation of a rearrangement of the constituent electrons of the gas atoms which occurs, in low vacuum tubes, if other factors of causation remain constant, at known voltages within a

Gas ionization in the vacuum tube is of great practical importance because of its effect on the current passing from filament to plate. Ionization, when it occurs, may operate within the range of the space current to increase “ conductivity ” of the tube, that is, the discharge from filament to plate, above what it would be at the same voltage in the absence of ionization, through the development of the positive ions, which pass to the cathode, and of the negative electrons, which pass to the anode. The ions facilitate the flow of electrons from cathode to anode and increase their number by impact on the former, whieh raises its temperature. The result is that, in low vacuum tubes, saturation with the blue glow effect is reached, other factors remaining constant, at lower voltages than in high vacuum tubes. Hence, in the range of voltage above ionization and below saturation, within which the tube is commonly operated, a low vacuum tube, because of the increase of current due to

But this advantage is accompanied by a serious disadvantage, especially when the tube is used for amplification, in that ionization produces variations in the electronic discharge from filament to plate, which correspondingly affect the current passing through the loud speaker circuit. Ionization is affected by the amount of gas in the tube, and hence by the degree of vacuum and the amount of occluded gas freed in operation by heat and bombardment. Since the discharge varies with the amount of ionization, the effective current in the loud speaker circuit varies with different tubes and with the same tube at different times; and critical adjustments of the current flowing to the filament are necessary to improve operation.

From what has been said, it is apparent that the problem of securing evenness or regularity of discharge from filament to plate and hence of current flowing through the loud speaker circuit is dependent upon the reduction of ionization in the tube, and this in turn is dependent, within certain ranges of limits, upon a number of variables, the more important of which are (1) the geometry of the tube, that is, its size and shape and the location of electrodes, (2) heat of the filament, (3) voltage of the filament, and (4) of vital importance here, amount of gas, that is, pressure within the tube. With the other variables controlled so as to remain approximately constant, as is practicable, reduction of pressure reduces ionization and increases steadiness of current and in turn raises the saturation point of the tube, permitting its use with higher than ionization voltages.

As in the low vacuum tube regularity or evenness of the loud speaker current was more or less imperfectly se

The desired reduction of pressure in the tube involves the use of methods for producing a high vacuum and reducing to a minimum the effects of occluded gas. By evacuating the tube by pump or other suitable means, and at the same time freeing it of occluded gas by heating tube and electrodes, and also, as may be done, by passing a current through.the filament, causing “bombardment” of the electrodes by electrons, a high vacuum tube is produced. By such procedure, the disturbing influence of ionization may be removed, with consequent stability of discharge. The result is of great importance, since by adaptation of the procedure to manufacturing methods, tubes giving uniform stability of current may be commercially produced, suitable for use in the complex mod

It is the high vacuum tube of this type which respondent says embodies the Langmuir invention. As a product or structure it differs from the low vacuum tube, of which the Fleming valve and De Forest audion are well known types, only in that the pressure has been reduced to such a point that there is no appreciable ionization, with the resulting constancy of current in the amplifier circuit.

In the light of the explanation given of the operation of the vacuum tube, we now examine the claims of the patent. The application, filed October 16, 1913, was pending for twelve years before it was issued October 20, 1925, a period which witnessed the most important beginnings and many of the chief developments of the radio art. The original application was for a process or method patent only. It contained five claims covering methods of obtaining a high vacuum in vacuum tubes and expelling occluded gas from them. These claims were all ultimately canceled. Other process claims, substituted by amendment, of which four only survived in the patent as issued, were amplifications of the original method and process claims. Late in 1913 Langmuir first made claim to invention of the tube as a structure or device, in four claims, all of which were amended one or more times. All but the third, which was amended four times, were canceled in 1925, the year the patent issued. There are twenty-eight claims for the structure or device in the patent as issued. Of these one was filed by amendment in 1913, one in 1917, nine in 1919, three in 1921, and fourteen in 1925. During the twelve years the patent was pending, there were sixty-seven amendments of specifications, of which forty-five were in 1925, Amended

The process claims cover methods of creating the high vacuum tube in the manner already described, that is, freeing the tube of occluded gas by heating tubes and electrodes and by electronic bombardment, at the same time evacuating the tube of air or gas by approved methods, such as the use of the Gaede molecular pump or chemical means. The court below did not rest its holding of validity of the patent on these claims, and respondent does not seriously urge their validity here. It suffices to say that an examination of the prior art discloses that, long before the earliest date claimed for Langmuir, the necessity for removing occluded gas from tubes or other electrical discharge devices in order to procure a high vacuum, and the methods of doing it by heating and electronic bombardment, were well known, as was the procedure for constructing the high vacuum tube by expelling occluded gas while evacuating the tube. An article by Duncan, American Electrician, May, 1896; one by Doane, Electrical World and Engineer, of May 21, 1904; the Dwyer Patent, No. 496,694, January 4, 1898, for a process for producing high vacuum in incandescent lamps or similar receptacles during, their manufacture; the Soddy Patent, No. 859,021, July 2, 1907, for the employment of certain reagents in the process of producing high vacuum; the Thatcher Patent, No. 1,028,636, June 4, 1912, application filed . March 30, 1910, for method of exhausting vessels; and an article by Lilienfeld in 1910, to be mentioned later, disclosed before Langmuir the essentials for producing a high vacuum, described in the present process claims. They were in use in laboratory practice by Millikan and others before 1911.

It was upon the claims for the high vacuum tube structure or device that the court below based its decision,

“ 2. A discharge tube having a cathode adapted to emit electrons and an anode adapted to receive said emitted electrons, the tube walls being fashioned or shaped to permit the direct passage of a useful proportion of said electrons from cathode to anode, the gas content or residue of said tube and the relation of the parts of the tube being such that the tube is capable of being so operated in a range below saturation and materially above ionization voltages that the space current is governed or limited by the electric field of said electrons substantially unaffected by positive ionization.”

, But this claim, as well as all others of the Langmuir patent, must be read in the light of the fact, fully accepted by the parties to this litigation, that electrical discharge devices such as the Fleming valve and the De Forest audion, patents on the latter of which expired in 1925, which were well known before Langmuir, comprise all the elements of the combination claimed except the presence within it of a high vacuum. It is conceded that if the requisite high vacuum be created in a De Forest audion, it becomes the high vacuum tube of the patent and is an infringing device if the patent is valid. The degree of the vacuum within the tube is therefore the crucial feature of the invention claimed. Langmuir, in describing in his patent the method of producing the device, says: “ The evacuation of the device should be preferably carried to a pressure as low as a few hundredths of a micron,

The characteristics of the discharge named by the inventor in the specifications “ in order to distinguish electron discharge devices made in accordance with my invention from the prior art ” are the following: (1) gas ionization absent or negligible; (2) cathode not heated by the discharge; (3) no blue glow or visible evidence of discharge; (4) 3/2 power relation of current to voltage; (5) discharge independent of degree of vacuum within intended limit for particular tube; (6) regularity and reproducibility. But all these characteristics may be summed up in the simple statement that in the tube of the patent, there must be an absence of harmful ionization; and since, as already indicated, harmful ionization disappears when the requisite vacuum is attained, the device or structure of the patent is one in which such a vacuum has been produced.

That the high vacuum tube was an improvement over the low vacuum tube of great importance, is not open to doubt. Even though the improvement was accomplished by so simple a change in structure as could be brought about by reducing the pressure in the well known low vacuum tube by a few microns, still it may be invention. Whether it is or not depends upon a question of fact, whether the relationship of the degree of vacuum within the tube, to ionization, and hence to the stability and effectiveness of discharge passing from cathode to anode, was known to the art when Langmuir began his experiments. If that relationship was then known, it re

That this relationship was known was the fact found by the District Court and not challenged by the opinion of the Court of Appeals. In 1910 Lilienfeld, in a paper published in Annalen der Physik, Vol. 32, on “ The Conduction of Electricity,” made a complete and explicit disclosure of the essentials of all the structures and methods of the Langmuir patent. The paper described methods of obtaining the “ extreme vacuum ” desired by freeing electrical discharge devices of occluded gas in the manner already described and at the same time evacuating the tube. He described the space charge effect, not mentioned in Langmuir’s original specification, but later recited in the claims of the patent, in the following language: “One can formulate more generally the conditions for high voltage and large current density as follows: The production of a state in which the volume density of the electrons carrying the current is as large as possible compared with the density of gas molecules in which there exists therefore a tendency for the formation of the maximum possible space charge in the path of the current.” To one skilled in' the art, this could only mean that increased effectiveness of an electrical discharge device, to which a suitable current is applied, could be obtained by raising the vacuum in the manner which the writer had described. He also stated that “ from a definite maximum density of the gas downwards, the discharge phenomena are independent of the gas density in the region investigated,” a statement equivalent to the fifth characteristic of the discharge in the Langmuir specification, namely, that it is independent of degree of vacuum within the intended limit for the particular tube.

Lilienfeld also deduced from meter readings and stated, the 3/2 power relation of current to voltage, as Langmuir

The very fact that Lilienfeld knew and described the methods of the patent for obtaining high vacuum carries with it as a necessary corollary that the device itself, apart from its functioning and use, is lacking in patentable novelty. Hence, invention, if any there be, is embraced in the discovery of the principle that discharges above ionization voltages can be produced without substantial ionization if the vacuum be sufficiently high, and the disclosure that the device of the claims constitutes suitable means for putting the principle into practice. But Lilienfeld; in his paper of 1910, disclosed that he obtained discharges free from the effects .of ionization, as Langmuir testified in interference proceedings in the Patent Office, and that he accomplished this through the attainment of high vacua by the very methods later described in the Langmuir patent.

Fleming, the inventor of the Fleming valve, in a paper read before the Royal Society on the conversion of electric oscillations into continuous current by means of a vacuum valve, February 9, 1905, pointed out the possibility of creating “ an ideal and perfect rectifier for electric oscillations ” by enclosing within a tube a hot carbon fila

“ It is apparent after a .review of the record that there is no single element which is broadly novel in the assemblage of elements making up an electron discharge device of the character defined in. the issue. An evacuated tube having therein an incandescent electron emitting cathode and an anode was old prior to the filing of Langmuir’s application, and methods of attaining high vacua, sufficient to give a relatively pure electron discharge in a properly designed tube were also well known and available to persons skilled in the art.”

The narrow question is thus presented whether, with the knowledge disclosed in these publications, invention was involved in the production of the tube, that is to say, whether the production of the tube of the patent, with the

Respondent recognizes the force of this objection to patentability, but seeks to avoid it by insisting that the invention claimed is not as we have described it, but that “ Langmuir’s invention consisted in taking out [of the tube] the gaseous conductor upon which the prior art

But if Langmuir’s invention is so to be defined, it is not the invention claimed by the patent.. Respondent puts forth as sustaining this definition, statements in the specifications of the patent, to the effect that in the device of the patent, in which gas ionization is absent, the discharge is “ distinct in its characteristics ” from the described discharge taking place in an ionized gas, and again that it is “ characterized by regularity and reproducibility with given conditions.” But, while these and many other statements in the patent indicate that high vacuum was an effective means of producing in the old tubes of the art the stable current which could not be produced in the presence of ionization, they do not suggest any discovery of a scientific truth that essentially different principles control the discharge in low vacuum tubes from those

If it were necessary to a decision we could not find that any such scientific truth is established by this record. Respondent, to support the contention, does not rely on evidence, but on a collection of more or less casual statements by various writers, made before 1915, to the effect that the gas or ionized gas of the low vacuum tube is a conductor. Before the, development of the electron theory, “ conductivity ” of substances was a convenient expression for explaining the flow of electric currents. Fleming, in a statement in 1906, already quoted, referred to the high vacuum as a good “ conductor ” if. a hot cathode was used. The present tendency is to ascribe the flow of current from a hot cathode through both high and low vacua to the flow or discharge of electrons. Millikan the eminent physicist testified that this theory was generally accepted before 1912. Langmuir himself so explained the flow of current in a gaseous tube in his specifications. The known truth is that current flows through both low and high vacua and is unfavorably affected by ionization in the former; but that the flow is due to conductivity of the ionized gas in one and to something different, pure electron discharge, in the other, is not established by the evidence before us. There is some testimony to the contrary. Nor is our attention directed to anything which suggests that Langmuir thought there was such a difference, or relied upon it to remove ionization effects, rather than upon the simple expedient of removing the gas known to be responsible for them.

Even if the asserted difference were established, it is no more than the scientific explanation of what Lilienfeld and others knew, before Langmuir, of the effect of the high vacuum on the discharge, and the methods and devices for procuring the vacuum. It is method and de

Only when invention is in doubt may advance made in the art be thrown in the scale to support it. If we were to assume that invention here was doubtful, we can find little to suggest that the high vacuum tube when produced satisfied a long felt want or that its present utility is indicative of anything more than the natural development, of an art which has passed from infancy to its present maturity since Langmuir filed his-application. There was little or no practical use for a high vacuum tube in 1913. The De Forest audion was not in general use and Langmuir did not see one until that year. The many amendments of Langmuir’s application during its long pendency, disclosing his uncertainty as to what he had invented, and the exhibits in this case, constitute a history of the development of the art, which indicate unmistakably that the resort to the high vacuum tube for discharges above ionization voltages was but the adaptation to the natural development of the art, by those skilled in it, of the scientific knowledge which had been accumulated by investigation and experimentation. When the need became apparent, De Forest and Arnold, as well as Langmuir, found ready at hand the knowledge which would enable one skilled in the art to satisfy it.

The court below, contenting itself with finding invention, said nothing of the finding of prior use by the District Court. We hold that this finding of the District Court was supported by the evidence and should have been given effect. As we have concluded that the Langmuir patent did not involve invention, we refer only briefly to the facts which establish prior use. In 1911 and until September of 1912, De Forest was in the employ of the Federal Telegraph Co. of California, then engaged in the commercial transmission and reception of radio messages, in which audion detectors as well as