Full opinion text
LEIBELL, District Judge. This action puts in issue (1) the validity and scope of a number of patents for electrical discharge devices and ultra violet lamps and (2) the infringement of the patents by the manufacture and sale of fluorescent and germicidal lamps. Patents in Suit Plaintiff, General Electric Company, charges that claim 3 of patent No. 1,790,153 issued to Hull, January 27, 1931, for an electrical discharge device, and claims 6, 13, 25 and 27 of patent No. 2,182,732 issued to Meyer, Spanner and Germer, December 5, 1939 for metal vapor lamps, have been infringed by the defendant, Hygrade Sylvania Corporation, in the manufacture and sale of fluorescent lamps. The Hull and Meyer patents are owned by General Electric. In a counterclaim the defendant Hygrade alleges that General Electric by the manufacture and sale of the General Electric fluorescent lamps and certain ultra violet germicidal lamps, has infringed claims 13, 43, 72 to 78 inclusive, and 80 of patent No. 2,201,817 issued to Charles G. Smith on May 21, 1940, for electronic space current discharge devices, and claims 1, 7, 11 to 13 inclusive, 25 to 30 inclusive, 41, 43, 48 and 49 of Reissue patent No. 21,954 to LeBel, reissued November 25, 1941, for an ultra violet lamp.. Hygrade is the exclusive licensee of the Smith and LeBel patents, owned by defendant Raytheon Manufacturing Company. The validity of still another patent was originally put in issue in .this litigation— patent No. 2,096,693 for a luminescent coating for electronic lamps, issued to J. L. Cox, on October 19, 1937 and owned by Hygrade. General Electric sought a judgment declaring the patent invalid. Hy-grade also counterclaimed on the Cox patent. Towards the end of .the trial Hy-grade conceded .the invalidity of the Cox patent and consented to a decree granting plaintiff’s prayer for a declaratory judgment and dismissing defendant’s counterclaim on the Cox patent. Prior to the trial the defendant Hygrade consented that another pleaded counterclaim, based on patent No. 1,982,821 for an electrode, issued to Marsden and Wheeler on December 4, 1934 and owned by Hygrade, should be dismissed. The Raytheon Manufacturing Company was made a party defendant by stipulation, because it holds the legal title to the Smith and LeBel patents. It had issued exclusive licenses to Hygrade on the Smith patent, in the fluorescent and germicidal fields, and had given Hygrade the right to sue thereon, shortly prior to the pleading of the Hygrade counterclaim in this action. A similar arrangement had been made between them in February 1940, in reference to the LeBel patent, a few months before the institution of this suit by General Electric. The Fluorescent Lamp In November 1937 the General Electric Company put on its special selling list a lamp which produced a new kind of light, a fluorescent lamp, generally acknowledged as the greatest advance in lighting since the Edison invention of the incandescent lamp. The white light of the fluorescent lamp, per watt of electrical energy consumed, is three times as efficient as the incandescent lamp. In the field of colored lights the fluorescent lamp is many fold more efficient per watt than colored incandescent lamps. For green it is 200 fold; for blue 50 fold. The colors include blue, green, pink, gold and red — in addition to daylight and white. Fluorescent lamps made in cylindrical tubes an inch to an inch and a half in diameter and varying in length between eighteen inches and forty-eight inches, give off their light over a large surface. They have less glare and give off less heat than an incandescent lamp of the same wattage with its more concentrated light. The eighteen inch fluorescent lamps are 15 watts; the twenty-four inch — 20 watts; the thirty-six inch —30 watts; the forty-eight inch — 40 watts (see Exs. 5 and 6). The great demand for fluorescent lamps for all kinds of lighting, in factories, in offlees and in the home, is shown by the sales of General Electric fluorescent lamps since November 1937. In 1938 General Electric sold about 180,000 fluorescent lamps; in 1939 — about a million; in 1940 over four and a quarter million; and in 1941 — 13,728,000 lamps. Hygrade copied in every detail the General Electric fluorescent lamps and began to market them in great quantities in 1939, falsely claiming for itself in extensive advertising that it was the creator of this “miracle in lighting.” How many million fluorescent lamps Hygrade made and sold is not in the record, but that their sales were extensive cannot be denied. The fluorescent material of the lamp is applied in the form of a phosphor coating on the inside of the elongated glass tube. When the ultra violet rays of 2536.7 Angstrom Unit wave lengths, emitted by the mercury vapor within the lamp, strike the phosphor coating it is activated and fluoresces and gives off light. The fluorescent lamps will operate on ordinary household and commercial A. C. current of 110-220 volts. The phenomena by which the ultra violet rays of 2536.7 A. U. are produced within the sealed glass tube is as follows: Within the lamp, sealed in at each end of the tube, is an electrode which changes from negative to positive, on a 60 cycle A. C. current, 120 times a second, so that at the time the electrode at one end of the lamp is negative (a cathode), .the electrode at the other end is positive (an anode). The electrodes are tungsten filaments coated with oxides of barium and strontium and are known as “Wehnelt” cathodes. The oxide coating helps the electronic emission from the cathodes so that they operate on less energy, start more readily and last longer. The tube is of ordinary window glass. It is filled with an inert gas, argon, and a globule of mercury. The pressure of the argon gas, about three or four millimeters, does not vary much with the temperature of the lamp. The globule of mercury gives off a mercury vapor and its pressure does vary with the temperature. At about 70° F. (21° C) the pressure of the mercury vapor within the lamp is about one micron (.001 of a millimeter). [Atmospheric pressure is 76 centimeters or 760 millimeters of mercury.] When the fluorescent lamp is in operation its temperature is 15-20° C. higher than that of the ambient air — a comparatively cold light. Taking into consideration the difference in temperature due to climate, the seasons, the time of day and the location of the lamp, the mercury pressure of the lamp, while in operation, may range from 4 or 5 microns to 39 microns. The metal ends of the lamp fit into sockets. As supplementary equipment there is a switch, a choke or resistance, and a time delay switch. When the main switch is closed to start the lamp, the A. C. current flows through the choke, through the electrode in the lamp at one end, through the time delay switch, and then through the electrode at the other end of the lamp, and back to the A. C. supply. In this way the electrodes are preheated red-hot while the current is by-passed through a circuit, in which the time delay switch is located. During this preheating process none of the current passes through the tube itself. Preheating reduces the required starting voltage. The preheating is for a predetermined interval of a few seconds until the time delay switch automatically opens its contacts. Thereafter the current passes from one electrode to the other, through the gaseous mixture within the lamp. The choke aids in starting the discharge and controls the value of the current flowing through the lamp. The electrical discharge consists of a stream of electrons — negative units of electricity — which flow from the negative electrode (the cathode) toward the positive electrode (the anode). When the lamp is in operation, the electrodes are of different voltage or electrical potential. The force which causes the electrons to move from cathode to anode is the electrical field which exists between the two electrodes, due to their different voltage. That difference is known as the voltage drop between them. The size and quality of the electrode is very important. Heated electrodes coated with alkali earth oxides give off most readily the greatest emission of electrons. An electrode thus heated is termed a thermionic cathode and the emissions therefrom “thermionic emissions.” General Electric lamps use preheated Wehnelt cathodes, which Hygrade copied. Ionization The pressure of the two gases in the tubes aids the passage of the current from cathode to anode. If the tube contained no gas it would be difficult for the current to flow from cathode .to anode at a low voltage, because of the presence of “space charge,” which is practically eliminated in the gas filled lamp. The electrons, emitted by the Wehnelt cathode when the lamp is in operation, act upon the gases (argon and-mercury vapor) within the .tube and cause ionization. This phenomena, ionization, has been explained by plaintiff’s expert, Dr. Clifton G. Found, about as follows: An atom consists of a positively charged nucleus surrounded by a number of electrons, the number depending upon the kind of atom it is. An argon atom nucleus is surrounded by 18 electrons; a mercury nucleus by 80 electrons. The negative charges of the electrons and the positive charge of the nucleus offset each other, so that the normal state of an atom is neutral. When the electrons emitted from the cathode in the gas filled tube collide with the neutral gas atoms, the collision may knock free an electron from .the parent atom upsetting the even balance of positive (nucleus) and negative (electrons) within the atom, and rendering the gas atom, after it has lost an electron, positive instead of neutral. The generation in this manner of positive gas atoms within the .tube is called “ionization.” That part of the tube where these positive ions neutralize a great number of emitted electrons is known as the “positive column,” in which the space charge is zero. The argon gas within the fluorescent lamp is itself sufficient to produce the ionization necessary to neutralize the space charge. This eases the passage of electrons from the cathode to the anode and thus fulfills one purpose for which the argon gas is placed in the tube. But argon gas does not give off ultra violet radiation, which is required to make the phosphor coating of the tube fluoresce. Excitation As the lamp in operation becomes heated the globule of mercury gives off a mercury vapor, containing atoms of mercury. If the force with which the electrons travelling from cathode to anode collide with the mercury atom is not sufficient to separate an electron of the mercury atom from its nucleus, but is sufficient to move an electron from its normal position in the atom to a position farther removed from the nucleus though still an integral part of the parent atom, then as the dislocated electron returns to its normal position in the mercury atom it gives up in the form of radiation the energy imparted to it by the colliding electron. The radiation thus created by the dislocated electron returning to its normal position in the mercury atom is ultra-violet. This phenomena of the electrons in the current through the tube disturbing the normal position of electrons of the mercury atoms is known as the “excitation” of the mercury. The predominant radiation thus produced is of a wave length of 2536.7 A U. [Angstrom unit is the term generally employed in physics in expressing the wave length of light. It is one hundred millionth of a centimeter. The visible range of spectrum, from violet to red, lies between 4000 Angstrom units for violet and about 7200 Angstrom units for red. The “ultra violet” is a radiation of a shorter wave length than the visible violet light and it is not visible to the human eye. Likewise, there are invisible radiations that have a longer wave length than visible red light; they are called “infra-red radiation.”] The voltage with which the electron hits the mercury atom in the fluorescent lamp determines whether excitation or ionization of .the atom takes place. If the electron has a speed of between 4.9 and 10.4 volts excitation takes place, if the electron’s voltage is 10.4 volts or more, the mercury atom will be ionized. Mercury is liquid at ordinary temperatures and while in the liquid state will have some vapor near its surface, depending upon the temperature of the coolest part of the tube. When -the fluorescent lamp is started it is generally at a temperature too low to ionize the mercury atoms quickly. As a result the argon atoms are the atoms first ionized and the electric discharge takes place first through .the argon. That is one reason why argon gas is used. The heat of the lamp in operation increases the pressure of the mercury vapor and the striking action of the electrons emitted from the cathode causes the excitation of the mercury atoms so that they give off the ultra violet radiation. In addition to this excitation of mercury atoms, some mercury atoms become ionized, so that the mercury vapor is both ionized and excited during the operation of the fluorescent lamp. The mercury vapor is the principal source of the radiation emitted. By regulating the energy with which the electrons collide with .the gas atom in a gaseous discharge device the relative extent of excitation and ionization may be varied. Once the mercury is vaporized by the heat of the lamp in operation on the low voltage A. C. current, both the excitation and ionization will be in the mercury vapor, because the ionization voltage for argon is about 16 volts, higher than that of the mercury vapor which is about 10.4 volts. There are several hundred times as many argon atoms per unit of volume in the lamp as there are mercury atoms, because of the difference between the argon pressure and the mercury pressure. The argon gas, in addition to supplying the medium through which the current is first discharged, later performs the important function of having its argon atoms get in the way of the positive mercury ions thus slowing down their speed as they journey towards the cathode, so that when the mercury ions strike the cathode they do so at a greatly reduced speed. Thus the argon gas is also a factor in prolonging the life of the cathode. The lamp is designed to keep the mercury vapor at the proper normal pressure. The mercury pressure depends on the temperature which of course is affected by the amount of current supplied. The. pressure of the mercury vapor within the lamp is such that it gives off the greatest amount of ultra violet rays of the most useful wave length, 2536.7 A. U. In a germicidal lamp, the tube is made of a special uviol glass, pervious to ultra violet rays, so that these rays may be used outside the lamp for germicidal and therapeutic purposes. Of course the tube of a germicidal lamp has no coating of fluorescent material. Hygrade charges that the General Electric 15 Watt, 30 Watt and 40 Watt germicidal lamps infringe the Smith and' LeBel patents. General Electric’s germicidal 15 and 30 Watt lamps are of the same size, shape and construction as the General Electric fluorescent lamps of the same wattage, except that the tubes are of a glass pervious to ultra violet rays and no fluorescent coating is used. “Fluorescent substances used in lamps absorb ultra violet energy, reradiate it at the longer wave lengths which are visible to the eye.” Hygrade Copied General Electric’s Fluorescent Lamps It is not necessary to review in detail the development of the fluorescent lamp at General Electric’s lamp laboratories. Dr. Thayer, who was in charge of this work, produced thirteen volumes of records of the'research and experimental work which he supervised in the years 1935, 1936 and 1937. His experiments included research into the proper size and shape of the .tube, the construction and location of the cathode, its preheating, current control, the use of pressure of gases, the various kinds of fluorescent materials, their mixture in a proper coating, the use of auxiliary equipment, and other details. One of the fluorescent lamps developed by General Electric during this research period was exhibited at the Convention of the Illuminating Engineering Society held at Cincinnati, September 3-6, 1935 (Ex. 47). The April 1936 issue of a General Electric publication, “The Magazine of Light” (Ex. 28) described the construction of its fluorescent lamps. They were not listed for sale until November 1937 (when they were put on a special schedule), because further efforts were being made by General Electric to perfect the lamp commercially. About 11,500 lamps were made in its laboratories, in the course of these experiments. On April 1, 1938, a complete line of fluorescent lamps of various sizes, colors and wattage, were placed on the General Electric regular stock schedules. Defendant Hygrade Sylvania was a competitor of General Electric in the manufacture and sale of electrical illumination equipment. If their staff had not seen or heard of the General Electric fluorescent lamp exhibited at the Cincinnati Convention in Septerflber 1935, they probably saw the account of the fluorescent lamp in the April 1936 issue of the “Magazine of Light,” for which Hygrade subscribed. One of the men in the Hygrade laboratories, Mr. J. Cox, in an office document dated May 15, 1936 (Ex. GG) entitled “April Research Report” stated that “During the month work was started on the development of a gaseous low pressure high efficiency 15 Watt fluorescent lamp.” The experiments did not result in any satisfactory lamps. “Lamp failures on life were due to sputtering of active material away from the cathode and the clean-up of gas to prevent restarting.” The principal trouble was with the 'cathode. He had some success in developing a fluorescent coating and method of applying it to the tube (Ex. GG-1; Ex. HH-1). October 8, 1937 there appears an entry by Mr. Cox in the Research Monthly Report (Ex. GG-2): “Due to the press of other work we have not been able to devote much time to fluorescent lamps. We have however made up a dozen lamps and built and installed six lamps in a hood over the Hy-grade lamp sign on the front of building A. The sign is burned each night from 5 P. M. to 8 A. M.” On December 16, 1937, the Chairman of the Hygrade Board wrote a letter (Ex. 12) to a Vice-President of General Electric asking for at least one sample of General Electric’s fluorescent gaseous discharge lamp to aid Hygrade,“in judging what the future of this product may be.” The letter ended with the statement that the Chairman of Hygrade would “handle the matter with proper discretion” and that General Electric’s Vice-President would have “no cause for any embarrassment as far as the use of the sample by our organization (Hygrade) is concerned.” The samples were accordingly sent by General Electric to Hygrade on January 14, 1938, in full confidence that Hygrade would keep its word and would not “make any commercial use of the sample” (Ex. 12-A). A further letter (Ex. 12-B) from General Electric to Hygrade referred “to the limitations iof the usage to which the samples are to be put.” The Chairman of the Board for Hygrade acknowledged the receipt of the samples, expressed his thanks for the courtesy, and wrote (Ex. 12-C), “I again repeat my assurance that you will not have any occasion to regret rendering us this service.” Exhibit NNN dated January 20, 1938 and Exhibit NNN-1 dated January 31, 1938, records of Hygrade’s Engineering Department, show the receipt of three General Electric fluorescent lamps and the prompt analysis by Hygrade of the structure of the lamps, in particular the cathodes. In October 1938 Hygrade put upon the market a line of fluorescent lamps that were exactly similar to the General Electric lamps. General Electric had improved its lamps between January 1938 and October 1938 and even these improvements were copied and embodied in the Hygrade product of October 1938. A comparison of the General Electric fluorescent lamps (Ex. 5) and the Hygrade fluorescent lamps (Ex. 6) shows how completely Hygrade copies the General Electric line — not only in the size and color of the bulbs, the socket and auxiliary equipment, such as the starting and preheating items,- but in the interior components, geometry and construction. Defendant’s only explanation for the copying was the necessity of standardization in the public interest, so that any consumer sockets would hold the lamps of both companies. But the standardization did not have to include the essential elements of the interior of the lamp construction, which made the General Electric fluorescent lamp a long-lived, commercially useful fluorescent lamp. Defendant asserts that it had no need to copy plaintiff’s General Electric lamps because Hygrade “had merely to copy its own two 1934 lamps.” The only two notebook entries relating ,to the August and September 1934 Hygrade experiment (read into the record) give no information from which one could begin to construct a fluorescent lamp. The August 13, 1934 entry is headed “Whitelight, high pressure mercury arc tests” and tells of applying a fluorescent material, aluminum oxide. The results were “very good at low intensities but no good at high intensities” — and the same result was obtained when a fluorescent red material was used. The September 6, 1934 entry states: “No. 3 fluorescent spectra: An attempt was made to add red light to the mercury spectrum by coating the inside of the lamp with a red fluorescent substance. Unless the mercury pressure was very low the red light from the fluorescence was not noticeable.” There is no mention of a rare gas, such as argon, in combination with the mercury. The Hygrade experiments tried to correct.the ghastly light of a mercury vapor lamp. The ■ experiments were unsuccessful and abandoned. The attempt to build up these meager records of Hygrade’s 1934 experiments by oral testimony, to give them the appearance of a successfully operated fluorescent lamp, failed utterly. The May 15, 1936, Hygrade memorandum entitled “April Research Report” (Ex. GG) shows that it was during the month of April that the “work was started on the development of a gaseous low pressure high efficiency 15 Watt fluorescent lamp.” Defendant Hygrade has not shown to my satisfaction that it had developed any kind of a fluorescent lamp in 1934. General Electric was the pioneer in developing a commercially useful fluorescent lamp — not Hygrade. We must not let the success of the General Electric fluorescent and germicidal lamps blind us in determining the issue of the validity and the scope of plaintiffs patents in suit. As Judge Learned Hand has recently warned in Derman v. Stor-Aid, Inc., et al., 2 Cir. 1944, 141 F.2d 580, 583: “An article may have an extraordinary success and may indeed be an invention of high merit, and yet that success and that invention may have nothing whatever to do with the combination described in the claims, but may depend upon elements, which, though added to those of the prior art, the patentee did not introduce in his claims, and perhaps could not have introduced. Although there is no better test than history, when used with proper circumspection, it is never safe to accept success alone as the measure of invention.” In an infringement suit the “comparison must be of the defendant’s device with the patent in suit, and not with plaintiff’s commercial device.” Tampax, Inc. v. Personal Products Corporation, D.C., 38 F.Supp. 663 at page 667, citing Hartford-Empire Co. v. Obear-Nester Glass Co., 8 Cir., 39 F.2d 769. See, also, S. S. Kresge Co. v. Davies, 8 Cir., 112 F.2d 708. If the General Electric fluorescent lamps did not embody the inventions described in the Hull and Meyer patents, then Hygrade in copying the General Electric lamps would not infringe those patents. And if the claims of the Hull and Meyer patents, in suit were invalid, .they could not be infringed. The Hull Patent No. 1,790,153 Plaintiff’s first cause of action for patent infringement is based upon claim 3 of patent No. 1,790,153 (Ex. 1) issued January 27, 1931, to Albert W. Hull of Schenectady, assignor to General Electric Company. The patent is for “an electrical discharge device and method of operation.” The application for the patent was filed in the Patent Office October 15, 1927, and bears serial No. 226,276 (Ex. L). Claim 3 of the patent as issued, reads as follows: “3. The combination of an electric current source having a voltage materially greater than fifty volts, an electrical discharge device connected thereto comprising a thermionic cathode, an anode, a container therefor, and a gas therein having a pressure within the range of several microns to several millimeters of mercury and means for maintaining the ion bombardment voltage with respect to said cathode less than a critical value characteristic of the nature of the gas in said container at which destructive disintegration of said cathode would occur.” The above claim was added to patent application No. 226,276 as claim No. 20 by an amendment filed June 11, 1928; that in turn was derived from a claim, No. 33, which had been filed as an amendment to Mr. Hull’s earlier application, bearing serial No. 594,370, on June 1, 1927. (See, Ex. MM-1.) The old claim 33 was allowed by the Patent Office December 31, 1927. On September 17, 1929, the applicant requested the Patent Office to cancel claim 33. In the “Remarks” of his counsel annexed to the request the following appears: “Allowed claims 33 and 34 have been cancelled because .their subject matter belongs in applicant’s continuation case, serial No. 226,-276 and the claims were placed in that case as claims 20 and 21 by amendment therein filed June 8, 1928.” Claims 20 and 21 at first were rejected but later were allowed in application No. 226,276. When patent No. 1,790,153 was issued claim 20 of the No. 226,276 application became claim 3 of the patent as issued. It is identical in language with old claim 33 of the prior application, No. 594,370. In the second paragraph of the specification of the Hull patent in suit, the inventor states: “The present invention relates to electrical discharge devices of the thermionic type. It is the object of my invention to provide an improved device of this type which is capable of a greater current carrying capacity, higher efficiency and a longer life than has been characteristic heretofore of devices of this character.” The “longer life” characteristic of the device pertains particularly to the thermionic cathode and its protection from disintegration by ion bombardment. In reviewing the art as known when his specifications were filed, Dr. Hull states that there were then in use two distinct types of thermionic power devices, one of which operated with a pure electron discharge and with practically no gas ionization because there is only a negligible gas pressure (vacuum devices). In this type, high voltages were required to overcome space charge and about one third of the transmitted energy was lost. The second type was a thermionic device “in which a gas is present at relatively high pressures, that is, pressures materially above one millimeter* of mercury, and usually as high as about five centimeters of mercury, although even higher pressures may be utilized.” In this second class of “concentrated arc devices” are the Tungar Rectifier and high pressure mercury lamps. The function of the gas in this second type, is to furnish positive ions to neutralize the space charge of the electrons and “allow large currents to pass from cathode to anode when the potential difference between them is only slightly greater than or even less than the ionizing potential of the gas.” Their cathode drop is “not materially greater than the ionizing potential of the gas.” Hull does hot here use the term “cathode drop” but he uses its equivalent, namely, “the potential difference between the cathode and the space immediately around it in the direction of the current flow.” The cathode drop is therefore such that the velocity of the positive ions “arrive at the cathode with very small energy, and their impact upon it causes no material disintegration.” The velocity of the ions in these tubes where the gas is at a high pressure is also reduced “by collisions between the ions and molecules of the gas as the mean free path of ions at these pressures is only a few thousandths of a millimeter.” The specification of the Hull patent goes on to state: “Between these two ranges of pressure, namely, the very low pressure of the pure electron discharge devices on the one hand and the relatively high pressures of the concentrated arc devices on the other hand, there is a range of pressures from about one micron to about one millimeter (1,000 microns) of mercury pressure which has never been considered practical for use in any thermionic devices of the power type. All attempts to use pressures within .this range have resulted in excessive disintegration of the cathode. In fact, it has generally been observed in the concentrated arc discharge range of pressures, that the lower .the pressure .the shorter has been the life of the cathode. When the pressure has been reduced to a millimeter or less, the cathode has lasted only a few hours.” The inventor then states in his specification that his present invention includes both a new apparatus and a new method of operating the thermionic discharge and that his discharge device contains gas ranging in pressure between about one micron and one millimeter. He then says that he has “discovered that thermionic tubes containing gas at a pressure in this range when suitably constructed and exhausted, may be operated with power currents for long periods without appreciable disintegration of the cathode”; that he has operated tubes of this low pressure diffuse discharge type for more than 4,000 hours without any material change in the appearance of the cathode or in its electron emissivity, Hull discloses, as the principal requirement of his invention, that the “positive ions which strike the cathode should have an energy less than a value represented by a critical or limiting voltage (referred to hereafter as the disintegration voltage) which varies with the atomic weight of the gas filling. The disintegration voltage is always greater than the ionization voltage of the gas. The disintegration voltage for mercury vapor is about 22 volts, for argon about 25 volts and for helium about 50 volts (the ionization voltages of these gases being 10, 15 and 25 respectively).” In addition to stating the basic principle of his device, the inventor explains the features that must be embodied in the construction of successful devices. He says: “The most important of these is that the cathode should be so proportioned with respect to the load or space current which the tube is designed to carry, that its electron emission in the absence of positive ion bombardment shall be equal to or greater than the maximum instantaneous value of the current through the tube.” He notes that devices of this type as made theretofore were inoperable because the electron emission of the cathode was itself inadequate, and that the device worked for a while only because the inadequate electron emission of the cathode was supplemented by electrons produced at the cathode by the positive ion bombardment, which in so doing disintegrated the cathode. He says that in accordance with his invention “The cathode emission is obtained at an operating temperature at which thermal vaporization is inappreciable and since disintegration by positive ion bombardment is avoided the cathode has a commercially long life.” His second requirement for the construction of successful devices is that the electrodes and all other parts of the tube should be thoroughly freed from any harmful gas and that the gas filling actually used should be “inert or chemically harmless with respect to the cathode.” His third requirement is “that the cathode shall be capable of being maintained at the operating temperature with a current that will not produce a magnetic" field sufficient to raise the potential between the cathode and the space immediately around it above the disintegrating value, and that the maximum potential difference between parts of the cathode shall be small compared with the disintegrating potential.” The first part of this requirement relates to the “cathode drop,” which will be considered later. His fourth requirement relates to the spacing between the electrodes and the general geometry of the device, which the inventor says “shall be properly related to the pressure of the gas or vapor content.” “The electrodes must be spaced apart far enough and the volume of the space available for ionization must be sufficiently great so that the number of ions formed will be sufficient to eliminate space charge.” Further the “product of gas pressure and distance between the remotest parts of the electrodes must not be sufficient to permit a glow discharge to pass between the electrodes in the absence of thermionic emission.” He then gives an example of the geometry of a device containing a mercury vapor, operating at a range of 1 to 40 microns for voltages materially above 100 volts. Hull says, too, that in one form of his device the cathode is so constructed as to prevent local hot spots on the cathode, so that there will be no deleterious concentration of the space current upon the cathode, and that “this feature is of particular utility in devices provided with cathodes coated with an alkaline earth oxide or other activating material.” The various figures (drawings) annexed to the Hull patent relate mostly to rectifiers embodying the invention, but figure 10 describes a form of lamp. The inventor explains it as follows: “Fig. 10 shows one form of such a lamp on a reduced scale, the elongated envelope 70 being shown broken as its length may be varied with the length of illuminating column desired. The cathode 71 and the anode 72 are spaced apart such distance ordinarily that the total voltage drop is several times the ionization voltage of the gaseous filling which may be neon, mercury vapor, or other gas having a desired luminosity. In a direct current lamp, such as shown in Fig. 10, the permissible gas pressure may be materially higher than in a rectifier. In the case of neon in such a lamp, a pressure of about two to five m.m. may be employed. Such a lamp about 50 to 60 c.m. in length, and about 2.5 c.m. in diameter may be operated at 110-120 volts with a luminous over-all efficiency of about 10 lumens per watt. In the case of a lamp, such as shown in Fig. 10, in which the length of the positive column is considerable, starting will be facilitated by applying high frequency in the known manner.” Di\ Hull is a scientist favorably known for his research in the field of electrical discharge devices. He has written a number of articles on this subject for scientific magazines, including publications of the General Electric Company Research Laboratory, some of which are in the File Wrapper of his patent application. In the File Wrapper, Exhibit MM-1, on application No. 594,370, which resulted in the issuance of patent No. 1,790,152, there appear the following scientific articles by Dr. Hull. 1'. An article read before the National Academy of Sciences on November 19, 1928, and later published in the General Electric Company Research Laboratory Magazine on the subject of “Control of an Arc Discharge by Means of a Grid,” written by Dr. Hull and one of his associates at the General Electric Laboratory, Irving Langmuir. 2. An article by Dr. Hull, on the subject of “Gas-filled Thermionic Tubes” published by the General Electric Company Research Laboratory under date of November 1928. This article is important and its subject matter is quite pertinent. The opening paragraph states: “This paper describes a fundamental principle of thermionic gas tube operation, by which cathode disintegration may be entirely avoided. A new type of cathode is also described which requires much less heat energy than any hitherto used. With these improvements hot cathode gas tubes appear to be practical, and their fundamental characteristics as lamps, rectifiers and ‘thyratrons’ are briefly described”. Page 2 of the article contains two paragraphs which show that the scientific fraternity knew the meaning of certain terms that are used in the specification of the Hull patent in suit. I quote the two paragraphs as follows: “The starting point of the developments described in this paper was the discovery that disintegration is produced only by the impact of ions of more than a definite kinetic energy. The critical value lies between 20 and 25 volts for the common inert gases. Any precaution which avoids the presence of ions faster than this will prevent disintegration. The simplest precaution is to adjust the circuit resistance so that the total ‘cathode drop’ does not exceed this critical value, which may be called the disintegration voltage. Fortunately, the disintegration voltage is in all cases considerably above the ionizing potential, so that it is possible to obtain the ionization necessary for carrying large currents without exceeding the disintegration voltage. In properly constructed tubes the necessary and sufficient condition for keeping the cathode drop within safe limits is that the cathode electron emission shall be equal to the maximum current demand.” The article then describes the operation of the disintegrating voltage in relation to a thorium-coated cathode. The paper relates certain experiments by Kingdom and Langmuir with cathodes made of cold thori-ated films and their determination of the number of thorium atoms removed per positive ion at different voltages. Dr. Hull explains similar experiments with hot filaments and large positive ion currents having somewhat lower voltages. He submits a table showing the condition and life of common cathodes (oxide coated — thoriated tungsten-pure tungsten) at various temperatures, and he points out the advantages of tubes containing gas and their greater use of the electron emission. In the File Wrapper on the earlier application „there is also an article by Dr. Hull, published by the General Electric Company Research Laboratory on the subject of the “Hot-Cathode Thyratron,” which is an “electrostatically controlled arc rectifier.” The inventor’s attorney, in discussing the nature of the plaintiff’s invention, stated in a paper filed in the Patent Office on June 7, 1928: “For the operation of such a power discharge a cathode must be provided which is capable of emitting the required current thermionically, substantially independently of positive ion phenomena. In other words, the cathode must be big enough and efficient enough to maintain the space current without the assistance of bombardment by positive ions.” The bombardment of the positive ions would release electrons from the cathode and thus assist in maintaining the required space current, but in doing so the ion bombardment would be destructive of the cathode itself,” and thus in a short time would kill the goose that laid the golden egg. Hull obtained the requisite thermionic cathode emissions by properly proportioning the cathode to the load or space current and by operating at a “temperature at which thermal vaporization is inappreciable.” This, together with the means he took to avoid destructive ion bombardment of the cathode, resulted in the cathode having a commercially long life. The destructive ion bombardment was avoided in Dr. Hull’s device by having its construction conform to the third requirement, as to the cathode drop. Dr. Hull specified that “the cathode shall be capable of being maintained at the operating temperature with a current that will not produce a magnetic field sufficient to raise the potential between the cathode and the space immediately around it above the specified disintegrating value,” which when mercury vapor is used “is about 22 volts” and “for argon about 25 volts.” Various claims of the Hull patent use the expression a “voltage drop at the cathode,” or “voltage drop in the neighborhood of the cathode.” Communications from the applicant’s attorneys to the Patent Office, while the application for the patent was under consideration, contained similar expressions. In the “Remarks” of the applicant’s counsel submitted under date of June 7, 1928, the following appears: “The circuit conditions must be such that the voltage drop at the cathode does not exceed a limiting voltage, herein called the disintegration voltage. New devices or new arrangements are not necessarily present in such a circuit. For example, the current may be limited by an ordinary resistance, or by the load itself, to a value at which thej cathode drop is below the disintegration voltage.” The expression in the patent, “potential drop at the cathode,” means the same thing as “voltage drop at the cathode” or “cathode drop.” An analysis of the construction of the fluorescent lamps, both plaintiff’s and defendants’, show that they operate for a satisfactorily long commercial life without the electrodes disintegrating, because the cathode drop is between 18 and 21 volts according to the size of the lamp, and in all instances is less than the limit of “about 22 volts” specified as the disintegrating voltage when mercury vapor is used, and the limit of “about 25 volts,” the disintegrating voltage for argon. Defendants’ attack on the method employed by Dr. Found, plaintiff’s expert, in determining the cathode drop, and upon his calculations is unconvincing. First it is intimated that the defendants do not understand the term “cathode drop” to mean what Dr. Found says it means. The patent itself and the scientific articles written by the inventor, Albert W. Hull, make clear its meaning. “Cathode drop” and “cathode voltage drop” mean the voltage drop at the cathode sheath, in the space immediately adjacent to the cathode, as explained by Dr. Found. The term has the same meaning as the “potential drop at the cathode.” Defendant’s experts knew its correct meaning. Indeed, the Smith patent, on which defendant Hygrade counterclaims, uses the expression “cathode voltage drop.” Defendants argue that a measurement by a probe within the tube, in the immediate vicinity of the cathode, would be more reliable than Dr. Found’s external method. If Dr. Found had inserted a probe in one of the Hygrade tubes (instead of measuring from the outside) it would have materially altered the conditions within the tube, if it did not completely destroy them. The defendant Hygrade could have made its own measurements on its own tubes, according to what it considered a better method. It is proper to assume that defendants would have done so, if they had believed that the experiment would contradict Dr. Found’s calculations or would show any fallacy in the teaching of the Hull patent on that point. Dr. Found applied his method in measuring the cathode drop in General Electric Company’s fluorescent tubes and got substantially the same results as in his measurements of the similar Hy-grade tubes. One of the defendant’s experts said that he did not know how to measure the cathode voltage drop, while the other expressed the view that the cathode drop was of the order of the ionization voltage of the gas in the tube, which would embrace Dr. Found’s figures. In defendant Hygrade’s fluorescent lamps every element of claim 3 of Hull’s patent is present. We have the following combination : (1) “An electric current source having a voltage materially greater than 50 volts.” Defendant’s fluorescent lamps operate on an alternating current of 110-220 volts. (2) “An electrical discharge device connected thereto.” The fluorescent lamp is an electrical discharge device. The lamp comprises: a. A “thermionic cathode,” i.e., the heated electrode which is emitting the electrons in the current stream, while the lamp is in operation. The thermionic cathode is well known to the defendants and their experts. The term is used in the Smith and LeBel patents on which defendant is counterclaiming. b. “An anode,” i.e., the electrode to which the current of electrons is traveling. c. “A container therefor,” i.e., the glass tube. d. “A gas therein.” In the fluorescent lamps there are two gases — argon and mercury vapor. Defendants devote a large part of their argument to prove that the Hull patent is limited to containers with only a single gas. I do not think it should be so limited. The Hull patent mentions both mercury vapor and argon. It does not say they should not be used in combination. The patent’s requirements are met in the fluorescent lamps as to both gases, in that the cathode voltage drop is less than the specified disintegration voltages for mercury vapor and argon. e. “Having a pressure within the range of several microns to several millometers of mercury.” The mercury vapor and the argon gas, in both the plaintiff’s and defendant’s lamps, are within this pressure range. The fluorescent lamps have a gas pressure of 3 to 4 millimeters. The mercury vapor pressure is between 1 and 40 microns. The defendants argue that what the inventor, Hull, staked off for himself was a range between one micron and one millimeter. The second type of thermionic device referred to in the history of the art, as set forth in the specification, was a thermionic device in which gas is present at a relatively high pressure “materially above one millimeter of mercury and usually as high as about, five centimeters of mercury.” It was in a range below that that Dr. Hull claimed his device would have a commercially long life where the other devices would not. I believe the range of the gas specified in claim 3, to wit, several microns to several millimeters of mercury is proper and is not inconsistent with the patent specification taken as a whole. At times defendant’s stand seems to be that under the Hull specification a gas pressure higher than one millimeter is permissible but not necessary. The language of claim 3 fixes its own range and is not inconsistent with the specification. f. “Means for maintaining the ion bombardment voltage with respect to said cathode less than a critical value characteristic of the nature of the gas in said container at which destructive disintegration of said cathode would occur.” As hereinabove indicated, the specification of the patent tells us that this critical or limiting value is characteristic of the nature of the gas used; and for mercury vapor it is about 22 volts, for argon about 25 volts. The specification also tells us that “The disintegration voltage is always greater than the ionization voltage of the gas and that the ionization voltage of these gases is 10 and 15 volts respectively.” The teaching is clear. Hy-grade Sylvania’s fluorescent lamps follow the teachings of the Hull patent and infringe claim 3. Fluorescent lamps use an oxide-coated cathode, not a thoriated cathode, so the defendants advance a number of arguments for limiting Hall’s claim 3 to thoriated cathodes. In the earlier Hull application (#594,370) there was considerable discussion of thoriated cathodes. Claim 3 of the patent in suit is the same as claim 33 of the prior application. From that the defendants conclude that claim 3 should be limited to a thoriated cathode. The argument is inherently weak. Further, no reference is made in claim 3 to any thoriated cathode. In the specification of the patent in suit, we find references to other types of cathodes. For instance, on page 3, line 46 of the printed patent, we read: “This feature is of particular utility in devices provided with cathodes coated with an alkaline earth oxide or other activating material,” and on the same page, at line 69, there appears: “Fig. 9 is-a graph of the volt-ampere characteristic of an arc discharge from an oxide-coated cathode, and Fig. 10 is a condensed view of a lamp embodying my invention.” The thoriated cathode is shown in only one of the figures in Hull’s patent in Fig. 1. Where details are given in the specification on any of the other figures, an oxide-coated cathode is indicated. It is of no special importance, that claim 3 of the patent in suit is the same as claim 33 of Hull’s earlier application, relating in part to thoriated cathodes. But it is significant that in the application on which the patent in suit was granted cathodes other than thoriated cathodes are included and that claim 3, by its language, is not limited to thoriated cathodes. The term used by Dr. Hull in claim 3 is a “thermionic cathode.” If he had intended to limit the type of cathode to a “thoriated cathode” he would have said so. And if he believed that the claim should apply only to an oxide-coated cathode, he would have so specified. The term “thermionic cathode” embraces both the thoriated cathode and the oxide-coated cathode. Where the inventor, in any of his claims under this patent, wishes to specify the metal content or composition of the cathode he does so specifically. In claim 2 he specifies “a thermionic cathode constituted of a body of sheet nickel”; in claim 5, “a thermionic refractory metal cathode provided with a material having a higher electron emissivity than said metal”; in claim 13,. “said cathode comprising a body coated with activating material of higher electron emissivity than said body”; in claim 14, “a thermionic cathode constituted of a base metal coated with a layer of higher electron emissivity than said metal.” It thus appears from the patent itself that the inventor in claim 3 deliberately chose the broader term “thermionic cathode.” But he defendants argue that the Court should give the narrow interpretation they seek, because of the presence of the word “critical” in the last clause of claim 3. If the word “critical” had been omitted from claim 3, the defendants admit there would be nothing to their contention. Defendants say that there is no “critical” value, where an oxide-coated cathode is used, although there may be a “limiting” value. That is a rather finely spun distinction. In either, case it means the disintegration voltage when a certain gas is used, as the specification clearly shows. There is a value (dependent upon the inert gas used) at which the cathode would be exposed to a destructive bombardment of the released gas ions (unless the teachings of the Hull patent are followed) whether a thoriated cathode or an oxide-coated cathode is employed. The “critical or limiting voltage” is the “disintegration voltage.” The “disintegration voltage” is a characteristic of the gas, not of the cathode. It bears a relation to the atomic weight of the gas filling. All this is explained in the patent specification. The “ion bombardment” is something to be controlled because of its effect on the cathode. The kinetic energy of the released gas ions is raised when they enter the field of the cathode drop, so that they impinge on the cathode with the energy thus picked up at the cathode drop. To control that energy and keep it below a certain range was one of Hull’s objectives. Assuming that the effect of the ion bombardment is not as destructive on an oxide-coated cathode as on a thorium coated cathode, it is at best a question of degree. The inventor’s discovery of a way in which to reduce the force of the ion bombardment to a minimum, would help the life of the cathode, in either case. Plaintiff’s expert, Dr. Found, definitely stated that there is a disintegrating voltage that is critical for an oxide-coated cathode, and that where mercury vapor is used, such as in Figure 9 of the Hull patent, the disintegrating voltage is the same for both an oxide-coated cathode and a thoriated cathode, to wit, 22 volts. To limit claim 3 to a thoriated cathode, as defendants now assert it should be limited, would run counter to the clear implication of the consent decree entered in December 1934, wherein the No. 872 A tube (a rectifier) of the defendant Hygrade, containing an oxide-coated cathode, was held to infringe this same claim 3 of the Hull patent. As a sweeping defense, defendant argues that the Hull invention does not contribute to the long life of the cathode, that it is the presence of the argon gas which produces that result. While the use of the argon gas at the right pressure in the fluorescent lamp furnishes protection to the cathode, because the argon gas aids in starting the lamp and thereafter its atoms slow down the movement of mercury vapor ions towards the cathode, the argon gas is not the sole protection of the cathode. In and of itself, the presence of the gas within the pressure range covered by the Hull patent, would not be sufficient to prevent the disintegration of the cathode, unless the invention of the Hull patent was followed in other respects. It is no answer to say that if the argon gas is removed, the lamp will not work. The gas is only one element. If you removed the electrodes or failed to properly proportion or space them, the lamp would not work. But that would not prove that the argon gas at the proper pressure is not an essential factor. Argon gas is necessary in the fluorescent lamp; but to know that fact is not enough in itself, as the failures recorded in the notebooks of Mr. Cox, a research worker in Hygrade laboratories, show. Finally, defendants argue that the Hull teachings are not followed because the electrodes in the fluorescent lamps do wear out, although they last for 2500 hours under ordinary conditions. Of course they do not last forever, but the fewer times they are started the longer they last. If they are permitted to burn steadily, they give their best service. It is in the starting that the greatest damage is done to the electrodes, because at that moment the cathode drop exceeds the specified disintegration voltage for mercury vapor, which proves the truth of Hull's teaching. But in ordinary use these fluorescent lamps will operate for more than two and a half times the commercial life of incandescent lamps, which have a commercial life of about 1000 hours. Hull’s invention in patent No. 1,790,153 is employed in the fluorescent lamp in order to prolong the life of the cathode. The other essential features of the fluorescent lamps will be considered in discussing the Meyer, Spanner and Germer patent No. 2,182,732. In an earlier suit by plaintiff, General Electric Company, against defendant Hygrade Sylvania Corporation, for infringement of certain claim of Hull patent No. 1,790,153, defendant consented to the entry of a final decree (dated December 18, 1934) adjudging claim 3 and other claims of said patent valid and infringed “by the defendant’s manufacture and sale of electrical discharge devices utilizing the inventions of each of said claims.” Defendant’s infringing device in that suit was a rectifier known as tube No. 872 A. As between the parties to this present suit that decree is conclusive on the issue of the validity of claim 3. Wilson v. Haber Bros., 2 Cir., 275 F. 346; O’Cedar Corporation v. F. W. Woolworth Co., 7 Cir., 66 F.2d 363. However, that decree does not bar the defendant from offering proof in this case as to the state of the prior art, for the purpose of showing the scope of claim 3 of the Hull patent, on the issue of noninfringement. Skelton v. Baldwin Tool Works, 4 Cir., 48 F.2d 221. .The Court may consider the state of the art to construe and narrow the claims of a patent, although a defendant is estopped from attacking the validity of the patent claims. Westinghouse Co. v. Formica Co., 266 U.S. 342, 45 S.Ct. 117, 69 L.Ed. 316. The defendants cite as prior art against Hull, a patent issued to George Stanley Meikle, also of Schenectady and also an assignor to the General Electric Company. The Meikle patent was issued May 9, 1916 and bears number 1,182,290. The original application was filed October 9, 1914 and was later divided. Meikle states that his invention relates to “the rectification of alternating current, of a current and voltage range comparable to the range of the mercury arc rectifier, and is embodied in a device having an electron-emitting cathode, and anode or anodes.” He also states that his device is distinguished “in one aspect from various prior devices containing an incandescent cathode by the presence of inert gas at a considerable pressure.” He adds: “Although no very definite lower limit of pressure can be assigned, for practical purposes the gaseous pressure should not be much below one millimeter of mercury as at very much lower pressures a rapid electrical disintegration of the cathode occurs.” The specification of the patent explained how the device is made. The main envelope consists of a ball with three arms for a full wave rectifier, or with two arms for a half wave rectifier. The envelope is first carefully evacuated and baked out at a high temperature. Then a quantity of inert gas is introduced in the envelope. “The gas is preferably at a relatively considerable pressure, for example, at a pressure varying from about one centimeter of mercury pressure upward to atmospheric pressure. No definite lower limit of pressure can be assigned, but the pressure should be high enough to largely suppress electrical disintegration of the cathode by the bombardment of ions.” This would put Meikle’s device in the class of concentrated arc devices mentioned by Hull as the second type of “thermionic devices in which a gas is present at relatively high pressures” and the high pressure serves as a protection for the cathode. It is clear from the specification of Meikle’s patent that his device was designed to operate with the inert gas at a relatively high pressure. His claims support that view. Claim 8 of his patent refers to a device with a filling of inert gas having at the operating temperature of the device “a pressure materially above one millimeter of mercury.” Claim 7 refers to a device with a filling of inert gas having at the operating temperature of the device a pressure of “at least about one centimeter of mercury.” Claim 2 refers to a pressure sufficiently high to give an electrical discharge emanating from the cathode, when at incandescence, the electrical characteristics of an arc. Hull’s specification recognizes the existence of rectifiers in which the gas filling is at a high pressure, but Hull’s device was designed to operate at a gas pressure of between several microns and several millimeters. What Meikle sought, according to his specification, was to keep away from the lower range of gas pressure which Hull showed could be used. Defendant says it follows Meikle and not Hull. The Meikle patent has expired. But defendant does not follow Meikle, who states in his specification (Lines 29 to 44 of p. 1) : “The electrical characteristics of my new rectifier are substantially those of an electric arc. “My invention is embodied in a device containing a cathode, of highly refractory material, such, for example, as tungsten, and an anode or anodes having a heat dissipating capacity enabling continuous operation at a given rated capacity at a temperature below about 727° C., at which temperature electron emission is relatively negligible, this device being filled with an inert gas of relatively appreciable pressure, preferably of the order of magnitude of atmospheric pressure.” The fluorescent lamps operate at a temperature of only 15-20° C. above the ambient air and the argon gas pressure is only 3 to 4 millimeters. Because of the great importance of fluorescent lamps, there is a “public interest” involved in this litigation, which required a careful inquiry into the validity of the Hull patent notwithstanding the December 1934 consent decree. I have made that inquiry and my conclusions are