AS early as 1894, in a paper on the subject of electrical radiation read at the Royal Institution, Sir Oliver Lodge explained the steps that it was necessary to take to screen electrical radiation. He pointed out that lor effective screening every part of the oscillating circuit must be completely enclosed in metal casing, and all the metal enclosures well connected together. He also explained that while small round holes in the casing did not matter, anything in the nature of a slot or chink, or the smallest “live” part of the circuit projecting through the casing, would allow the radiation to pass. The ignition system of a petrol engine generates an oscillating discharge, sending out electrical radiation, and to prevent this radiation interfering with a neighbouring radio receiver it is necessary to enclose the whole ignition circuit—magneto, cables and sparking plugs—in metal casing.
Lodge, A.M. (1933), "Radio Screening of Sparking Plugs: The Design and Construction of a Compact, Adequately Insulated, Screening Cap Fully Described", Aircraft Engineering and Aerospace Technology, Vol. 5 No. 5, pp. 116-116. https://doi.org/10.1108/eb029681
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