Harmonic lure, alarm, underworld muse, integral danger—all these facets of the classical Sirens stalk the evolution of their technological avatars.
In the beginning, sirens made music. John Robison—a moon-faced eighteenth-century physicist and mathematician who collaborated with James Watt on an early steam car and was a prominent member of the Edinburgh Philosophical Society who became, in later life, an obsessive conspiracy theorist—wanted to measure the number of air pulses that went into producing a given pitch. A few years after completing his paranoiac masterwork, “Proofs of a Conspiracy against all the Religions and Governments of Europe, Carried on in the Secret Meetings of Freemasons, Illuminati and Reading Societies,” Robison constructed a stopcock that could rapidly open and shut the passage of a pipe. He then attached this apparatus to the pipe of a conduit leading from the bellows to the wind-chest of an organ. Opening the cock allowed air to flow along the pipe into the organ. In addition to discovering the invention’s pitch-gauging capacities, he found that by varying the speed at which the cock opened and shut he could create different sounds. At 720 times a second, Robison declared, the “smoothly uttered” sound was “equal in sweetness to a clear female voice.” Twenty years later, Cagniard de la Tour refined Robison’s device so that it now comprised two discs, each pierced by one hundred oblique apertures and mounted on a pneumatic tube. The lower disc was stationary, while the upper one could spin. When air was forced through the holes of the bottom plate, the upper one revolved. Sometimes the two sets of holes aligned, allowing a puff of air to pass through, sometimes they did not; the succession of air puffs produced a musical note. De la Tour called the instrument a “siren” because it was equally capable of making its music when water passed through it rather than air, or when the whole instrument was submerged. Listeners marveled not only at its pleasing harmonics, but also at how loud the siren could be.
It wasn’t until the late 1860s that Professor Joseph Henry, a dominant presence on the United States Light-house Board, began fiddling with de la Tour’s instrument to develop a steam-powered siren for use as a fog signal. Henry’s device worked by driving steam through slits in two disks: one fixed, one mobile. However, Henry’s mobile disk was placed in the throat of a large trumpet. At sufficient pressure, steam made the mobile disk spin 2400 times a minute, producing 480 vibrations per second and creating a sound that could be heard up to thirty miles away. For the first time, the siren moved from being a source of beguiling song to serving as an engine of alarm. Indeed, a series of tests in the mid-1870s comparing sirens to guns, horns, and whistles determined that sirens traveled further in space and penetrated more local noises than any other acoustical signal.14