. Earth, sky, and sea . Fig. 16. Diagram of the magnetic valve detail. As long as an electric current runs through the coil d, the iron- shot is magnetized just where the tube narrows. In this way it is trans- formed into a more or less rigid mass which acts as a plug. Thus the pellets cannot flow away. As soon as the current is cut, the pellets are demagnetized and flow like sand in an egg-timer. It is enough to switch on the current to stop the flow at once. It is clear that the principle is very simple. [152]

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