The whistle in the base of the fire engine has a slide which, when moved back and forth by a handle underneath the engine, changes the length of the whistle cavity. This, of course, changes the tone of the whistle up and down making it sound like a siren.

This is my most difficult whistle project. You should consider yourself a moderately skilled wood worker. Getting the slide to fit the whistle bore tightly enough to let the whistle work and loosely enough so it won't bind is a job for the most patient wood workers only!

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