This acoustic apparatus produces sounds of the desired acuteness and measures their frequency by means of a stopwatch.
Sirens are usually made of brass and are composed of a cylindrical chamber into which a constant stream of air is introduced through a nozzle that comes out of the bottom to which one of the outlets of a bellows is connected.
The specimen exhibited here is made of brass, it has an overall height of 20 cm and it is mounted on a round, wooden base painted black (diameter 8.2 cm, height 4.6 cm) by means of a central staff with a nozzle through which the air is pumped.
The cylindrical chamber is 2.6 cm in height and has a diameter of 4.5 cm. The rotating disk is of the same diameter and has twenty-five holes. ...continues