The opinion of the court was delivered by: FORMAN
Plaintiff filed an application for a patent on June 26, 1926, which was allowed on July 7, 1931, under number 1,813,334. The purpose of the invention as recited in the patent "is to provide a single control for both the filament and plate batteries of an audion circuit, whereby the filaments may be lighted prior to the circuit on the plate being closed, so that reactivation of the audion may take place without removal from its normal position in the circuit".
Two claims were allowed for the patent, as follows:
"1. In an audion circuit in which a switch is interposed in the common leg of the plate and filament circuits, the method of maintaining the activated condition of the filaments which comprises operating the switch to first close the filament circuit, and after an appreciable time further operating the switch to close the plate circuit without opening the filament circuit.
"2. In combination with an audion circuit including plate and filament circuits and separate energizing means for said plate and filament circuits, a three pole control switch having a movable element to electrically connect or disconnect said poles, one of said poles being connected in the common leg of the plate and filament circuits and the other poles respectively connected one to each of the remaining terminals of said energizing means, said movable element being actuable to first close the filament circuit and thereafter to close the plate circuit without opening the filament circuit, said movable element being retainable in either of its two circuit closing positions."
Plaintiff charges that his said patent has been infringed by the defendant because it incorporated his invention in its Western Electric 23-A radio transmitter and in its Western Electric 355-E-1 radio transmitter.
The defendant contends that plaintiff's claims are not infringed in its devices; that in view of the file history plaintiff's claims cannot be construed broadly enough to be infringed and in any event the plaintiff's claims are invalid in view of the admitted prior knowledge.
In 1923 plaintiff was granted licenses for limited commercial and experimental broadcasting. He claims that in operating his station in Trenton, New Jersey, he experienced trouble when transmitting tubes used by him were burned out through the inadvertent closing of the plate circuits prior to the application of energizing current to the filaments. This was in the days when receiving sets were battery energized and transmitting sets were similarly energized or with direct current generators. As a consequence of his experience, plaintiff conceived the idea of employing a knife switch supported on a base by means of a hinge clip followed by an intermediate clip and an outer clip. The clips were forked or bifurcated so that the switch might engage them in sequence, the first application of the switch thrusting it into the hinge clip, the second into the intermediate clip and the third into the outer clip. The hinge clip was connected to the minus A binding post. The intermediate clip was of greater length than the outer clip and was connected to the minus terminal of the filament battery. By engaging the switch in this clip the circuit on the filament battery would be closed ahead of closing the circuit on the plate battery of which the minus terminal was connected with the outer clip. if the switch was moved into engagement with the intermediate clip and permitted to remain in position, the audion filaments would be energized with no potential from the plates. The patent taught that the switch should be permitted to remain in this position for a short period, "say three or four minutes", so that the "coating of the filaments will be caused to flow back to them from the plate or elsewhere that it may have been deposited in the tubes.
The filaments having thus been permitted to burn a short while to restore their coating, a further movement of the switch into engagement with the (outer) clip 22 will result in closing the plate battery circuit".
At the trial plaintiff contended that it was his purpose to preserve the original condition of the tubes so that reactivation in its strictly technical sense would not be necessary. He stated that it was not his purpose to reactivate tubes in the sense that reactivation is now or possibly then was understood and conceded that the term "reactivation" may have been inadvisedly used by him. He further conceded that reactivation of filaments in the strictly technical sense of the term was known prior to the date of his invention and he admits that it was known to be advisable to energize the filament prior to closing the circuit that would apply direct current to the plate. He states that his invention did not lie in the provision of means for using either of these two expedients although it had the advantages of both. The plaintiff claims he first saw the possibility of preserving the original condition of the tube by the systematic application of filament and plate voltages, and a means for carrying out the method. He says that it is clear from his patent that this was its purpose despite the use of the "possibly ill-advised word 'reactivation'".
Plaintiff commercialized his invention in the form of a switch accompanied by a circular prescribing the method for its use and according to his testimony he sold about fifteen hundred of them. The directions contained in the circular read as follows:
"Aways place the blade of switch in position 'A' for a minute before using the set; then to position 'B' and tune in your station. Your tubes will not be shocked and your filaments will not throw away needlessly the thoriated element. The lighting of the filament before applying the plate voltage is the best known radio practice. Also, it permits full expansion of the filament before it is put to work discharging its electrons. This procedure insures longest possible life of your tubes without overloading them to obtain good clear long-distance signals.
"If you do not use the 'Minus' switch as directed, you can only blame yourself for inferior results.