James Douglass and George Slight worked on developing modern sirens (jan 1, 1877 – jan 1, 1880)
Description:
'These modern mechanical sirens use two concentric cylinders, which have slots parallel to their length. The inner cylinder rotates while the outer one remains stationary. As air under pressure flows out of the slots of the inner cylinder and then escapes through the slots of the outer cylinder, the flow is periodically interrupted, creating a tone."(unknown)Added to timeline:
Date:
jan 1, 1877
jan 1, 1880
~ 3 years