283 U.S. 664 (1931), 630, DeForest Radio Co. v. General Electric Co.

Docket Nº:No. 630
Citation:283 U.S. 664, 51 S.Ct. 563, 75 L.Ed. 1339
Party Name:DeForest Radio Co. v. General Electric Co.
Case Date:May 25, 1931
Court:United States Supreme Court

Page 664

283 U.S. 664 (1931)

51 S.Ct. 563, 75 L.Ed. 1339

DeForest Radio Co.


General Electric Co.

No. 630

United States Supreme Court

May 25, 1931

Argued May 1, 4, 1931




1. Patent No. 1,558,436, to Langmuir, for a high-vacuum discharge tube, used as a detector and as an amplifier in radio communication and telephony, and for the process of making it, held invalid for want of invention and because of prior use. Pp. 676, 678, 682.

The tube in question corresponds structurally with earlier low-vacuum tubes used as detectors and amplifiers, and, as a device or product, its only essential difference from them is in its higher vacuum, produced in the course of manufacture by mechanical exhaustion aided by heat and electronic bombardment. In consequence of this removal of gas, the tube is not subject to the gas-ionization which renders the other tubes uncertain and inefficient, especially when they are used as amplifiers, but is capable, within its limits, of producing a stable discharge when operated at a fixed voltage, and will operate at much higher voltages than the earlier tubes. This tube is an important improvement over the earlier ones, but the patent cannot be sustained, because, as the District Court found and as the evidence shows, the process for creating high vacua in tubes was well known and practised in the art, and the fact that the ill effects of ionization in such electric discharge devices could be removed by increase of vacuum was so known and disclosed in science that the application of that means for improving the earlier devices involved not invention, but only the expected skill of the art.

2. The question is not whether the prior art had made a practicable high-vacuum tube, but whether it showed how one could be made, and demonstrated and disclosed the relationship of the discharge to the reduced pressure. P. 682.

3. The evidence does not establish that the flow of current is due, in a low-vacuum tube, to the conductivity of ionized gas, and, in a high-vacuum tube, to something else -- pure electron discharge; nor does it appear that the patentee thought there was such a distinction, or relied upon it to remove ionization effects, rather than upon the simple expedient of removing the gas known to be responsible for them. P. 684.

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4. A scientific explanation of a known method and device is not patentable. P. 684.

5. Value and general use of a device cannot sustain a patent if the lack of invention is clear. P. 685.

6. The resort to the high-vacuum tube of the patent, and its present utility, are explained as the natural development of a new art through the adaptation to it of scientific knowledge that had been accumulated through investigation and experiment. Id.

7. The prior use of an invention that will invalidate a patent need not have been accompanied by knowledge of the scientific principles involved in the invention. P. 686.

4 F.2d 931 reversed.

Certiorari, 282 U.S. 836, to review a decree holding a patent valid and infringed and reversing a decree of the district court, 23 F.2d 698, which had dismissed the bill upon the grounds of want of invention, prior invention, and prior use. The court below, by an unreported per curiam opinion of October 3, 1929, had at first affirmed the dismissal upon the opinion of the district judge. The contrary decree here under review was rendered after a reargument.

Page 669

STONE, J., lead opinion

MR. JUSTICE STONE 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

Page 670

the alleged invention is exemplified in high vacuum tubes of familiar use as detectors or amplifiers in the art of radio communication and telephony. Correct appreciation of the contentions made requires, at the outset, an understanding and some exposition of the scientific principles which it is agreed are brought into play in the high vacuum tube or which at least are accepted as working hypotheses accounting for its operation.

A radio tube of the audion or three electrode type consists 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 loudspeaker. In operation, the filament is heated to incandescence by passing [51 S.Ct. 564] 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 loudspeaker circuit. The sounds given out by the loudspeaker are produced by variations in the current passing to it. Radio amplification depends on producing, in the more powerful current of the loudspeaker 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

Page 671

effective potential of the plate with corresponding variations in the loudspeaker circuit. The number of electrons emitted by the filament is determined by its temperature. But the current passing through the plate loudspeaker circuit depends on the number of electrons drawn from the filament to the plate, and this, in turn, depends on the voltage of the current passing to the filament. When it is high enough to force all the electrons emitted by the filament to pass from filament to plate, increase in the voltage at the filament will not produce an increase in current in the loudspeaker circuit, and the tube is then said to be "saturated." As successful operation of the tube depends on the response of the loudspeaker current to changes in voltage effected by the voice or input current, the tube is most efficiently operated at a voltage of a range below saturation, and a current within this range is known as the "space current."

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

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range of from 20 to 30, but varying somewhat with different gases. The atom, according to present day scientific theory, is composed of an electrically positive nucleus, around which revolve at high...

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