591

Fig. 6.-British patent to Bairsto, et al.

The distributor screen or shield 14 is shown as secured to the distributor in the manner just described. The screen as shown does not cover the lower portion of the insulating material of the distributor block and it is therefore incomplete. This patent does not disclose a complete shield entirely closing the ignition system and does not suggest to those skilled in the art the use of the braided shielding on the ignition leads as forming a path for the return flow of current from the spark plugs.

42. The articles entitled "Wireless Navigation for Aircraft" (defendant's Exhibit 4) and "The Elimination of Magneto Disturbance in the Reception of Wireless Signals on Aircraft" (defendant's Exhibit 4a) by Captain Robinson, both discuss problems relating to radio reception on aircraft and dealing with the interference produced by the magneto ignition systems.

The only reference found in the first article is the statement that

It is possible to use short wave stoppers to cut out these waves, but by far the most efficient method of elimi

Special Findings of Fact

123 C. Cls.

nating this disturbance is to screen the whole magneto system.

The second article discusses various experiments relating to this problem and also suggests a complete shielding of the magneto ignition system. With respect to this shielding the article continues as follows:

The magnetos themselves should be encased in metal shields. The high-tension leads from the magneto to the sparking plugs should be run in earthed tubes. The same applies to the low-tension leads. When this is done properly there is no trace of magneto disturbance in the most sensitive receiving system. It is not always necessary to put the magnetos in special metal cases. This applies in the cases where the engines are completely cowled. The earthing of the metal shields of the high-tension and low-tension systems is most important. It is not sufficient to bind earthing wires round the metal shield and the earth system if these metal parts are covered in grease. Good earths should be made to the common potential of the metal framework of the aeroplane, consisting of the engines, tanks, and bracing wires. The metal casing of the H. T. leads must be earthed every 18 inches or 24 inches by as short leads as possible. This applies also to the lowtension leads. This earthing at various places provides closed circuits which form oscillating circuits for very high frequencies, and thus help to absorb the short waves radiated from the magneto system.

There is no disclosure in the article relative to the use of the shielding as a return path for the ignition current to the spark plugs.

43. "The Year-Book of Wireless Telegraphy & Telephony" (defendant's Exhibit 5) contains an article relating to the problems of the installation af a radio telephone on aircraft. In this article, after a discussion of the oscillatory discharge occurring in the gap of a spark plug and the high-frequency waves thus generated and radiated therefrom, the following is stated with reference to shielding:

2. The second method is to screen completely, or enclose in metal, the whole of the component parts of the magneto system. This is a much more simple method when it is carried out while the engine is being built, and before it is installed in the aeroplane, but a very

591

Special Findings of Fact

different matter when once the machine is completed without it, as those who have seen the amazing complication of an aero engine will realise.

A complete specification for carrying out this work has recently been issued by the Marconi Company, which ensures that no magneto noise will exist on machines where their system is employed. The principle employed in this specification is, firstly, to wire the engine with special copper braided ignition wire; secondly, to provide an effective screened aero plug, which has been designed in conjunction with the Robinhood Engineering Works, the well-known K. L. G. manufacturers, and thirdly, totally to enclose the magnetos with an iron cover on which a coating of copper has been deposited. This article does not disclose or suggest to those skilled in the art the use of the shielding as a return path for the spark plug currents.

44. United States patent to Gill #761,372 (defendant's Exhibit 7) discloses a portable electric gas lighter. This device, which is shown in Fig. 1 of the patent and is reproduced herewith, consists of three basic elements.

The lower or bottom element, as shown in the drawing, consists of a tubular metallic battery case containing what is referred to in the specification as "a well-known form of dry battery cell." The customary voltage of a dry battery cell is 12 volts, and for the use involved in the Gill patent those skilled in the art would consider that a battery with a voltage between 12 and 10 volts would be sufficient.

The second element extends upwardly from the top of the metal battery case and consists of a tubular metallic member of relatively small diameter as compared to the upper case. This member carries at its top the gas lighting device and its function is to provide an extension of sufficient length to enable the operator to readily reach a gas burner. This tubular member encloses a coaxially located insulated conductor.

The third element consists of the lighting device which is a small coil of wire stated to be "made of platinum or other suitable material" and of such size as to be made incandescent when current from the battery is passed through the wire. Flow of current from the battery to the lighting coil

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Special Findings of Fact

is controlled by a switch button which projects outwardly from the combination handle and battery case.

The lighting coil is mounted upon an insulating block attached to the upper end of the tubular extension. The lighting coil itself is protected by means of a perforated cap. The specification is silent as to the material from which this cap is formed. This could be made from either metal or ceramic material.

When this device is operated by pressing the switch in the handle, current flows from the enclosed battery or generating device through the coaxial conductor to the receiving device or lighting filament and returns to the battery through the walls of the tube and battery case. The Gill disclosure shows these walls to be structures of appreciable weight and thickness, and since their electrical resistance is therefore low, these exterior walls form a reasonable approximation to equipotential surface.

45. United States patent to Gardy #873,123 (defendant's Exhibit 8) discloses a massage device consisting of a metallic battery casing containing dry batteries upon the top of which is mounted a small electric motor. A massage implement is mounted upon the shaft of this motor. The motor is enclosed in a casing which the specification states may be a twopart casing if desired.

The specification does not state of what material this casing is made. No coaxial transmission line is disclosed between the battery and the motor.

46. In 1921 and succeeding years Marconi's Wireless Telegraph Company, Ltd., was engaged in the manufacture, sale and distribution of radio receiving and transmitting sets especially designed for installation on aircraft. In 1921 there was prepared and printed a handbook entitled "Marconi Aircraft Telegraph and Telephone Apparatus: Its Installation, Testing and Maintenance." The "File Copy" of this handbook has been produced from the Marconi Company's files and is in evidence in this case as defendant's Exhibit 15.

The purpose and intent of this booklet, which will be hereinafter referred to as the Marconi handbook, was to provide detailed instructions for the installation, testing and mainte