  Consider an electron drifting in a gas toward a collection electrode. A
common misconception is that the electron produces a detectable signal only
upon arrival at the electrode. In fact, the situation is quite the opposite.
The electron induces a detectable current in the electrode as soon as it starts
moving through the gas. This induced current vanishes when the electron arrives
at the plate. To illustrate this phenomenon experimentally, we use a gas-filled
parallel plate ionization chamber and a collimated $^{241}$Am alpha source,
which produces a track of a fixed number of ionization electrons at a constant
distance from the collection electrode. We find that the detected signal from
the ionization chamber grows with the electron drift distance, as predicted by
the model of charge induction, and in conflict with the idea that electrons are
detectable upon arrival at the collection plate.
