“But that’s just my puzzle,” French returned. “That’s exactly what seems to have been done.”
“Well,” Mr. Illingworth answered with a smile, “you may take it from me that it wasn’t.”
“Then in the case that I have described, the breakdown must have been a pure accident?”
“I should say, absolutely. Mind you, I don’t say that a breakdown couldn’t be faked without leaving traces. It could be. But not so as to stop the car then and there. The concealed injury would take time to develop.”
“That’s a bit cryptic, isn’t it? Can you make it clearer to a lay intelligence?”
“Well, it is possible to damage the insulation by jamming a needle into the armature winding between the wire and the iron core, and if you’re careful it’ll leave no mark. But it won’t disable the magneto straight away. In fact, the car will run as usual and it may be a considerable time before any defect shows. But sparking takes place at the injury, perhaps at first only when the engine is working specially hard. This causes carbonisation of the insulation, leading eventually to complete breakdown. The car begins to misfire and it gradually grows worse until it won’t run at all.”
“I follow you. I may take it, then, that it is possible to cause a breakdown without leaving a mark, but that this is a comparatively lengthy process and cannot be done at a given time.”
“That’s right.”
“Suppose the winding was short-circuited as you describe, could an electrician afterwards tell what had been done?”
“No. It might have happened through some carelessness in the original winding.”