Early in 1915 I had the honour of delivering to one of the largest Engineering Societies in the Midlands, a lecture on "The High Tension Magneto," which is—superficially at least—familiar to all those associated with the Aeroplane and Allied Industries. The present paper is really a continuation of my earlier effort, and, being presented to an Aeronautical Society, I shall naturally make special reference to the high-tension aeroplane type of magneto. The amount of technical literature on this subject available at the present moment is very meagre. It is therefore hoped that this contribution will have the effect of initiating a healthy discussion of ignition problems and stimulating the interest of all members of the engineering industry who are either directly or indirectly interested in the matter.