A device designed to be placed in the mouth and blown, or driven by steam or some other mechanism, to make a whistling sound.
A lovely crisp exhaust: a feeling of almost unlimited power combined with complete freedom of running: and, to crown it all, a most melodious and wholly American chime whistle—these were my immediate impressions as we stormed rapidly out of Göttingen, intent on winning back some of the lost time.
One thing I took great care to observe was obedience to the "whistle" boards which crop up with great frequency, for failure to sound the whistle, if observed by the gendarmerie, can bring about serious consequences.