As early as the 18th century physicists were experimenting with tones produced by the effect of flames on nearby glass tubes, and in 1873 the physicist Georges Frédéric Eugène Kastner developed a keyboard pyrophone.
More recently, singing flames have been featured in mixed media works by artists such as Andreas Oldörp, whose Singende Flammen (1988) was installed in a preexisting tunnel beneath Hamburg’s Hans-Albers-Platz. Composers who have used singing flames in their work include Alvin Lucier.
This according to “Singende Flammen: Andreas Oldörps Arbeiten zwischen Experiment und Installation” by Volker Straebel (Neue Zeitschrift für Musik CLX/2 [März-April 1999] pp. 45–47).
Above, Kastner’s pyrophone; below, two views of singing flames in Sydney’s Darling Harbour in 2011.
In 1950 a pipe organ built to the specifications of Adriaan Fokker (1887–1972) with octaves divided into 31 steps was inaugurated at Teylers Museum in Haarlem. The instrument originally enjoyed considerable fame, and a lively circle of composers and performers developed around it.
Since 1942 Fokker, a physicist who had studied with Einstein, had been occupied almost exclusively with music-theoretical subjects. His interest was particularly captured by the writings of Christiaan Huygens (1629–95), who advocated the adoption of just intonation. This theme became the backbone of nearly all Fokker’s music-theoretical publications.
To turn his theories into sounds, Fokker had a small organ built in 1943. This instrument was the prelude to the realization of his greatest dream: a pipe organ with 31 tones per octave. This instrument was built starting in 1945 in close cooperation between Fokker and the organ builder Bernard J.A. Pels (1921–96).
Then for years the organ was forgotten; it was even dismantled and placed in storage. But since 2009 the instrument sounds again, in the Muziekgebouw aan ’t IJ in Amsterdam. And again composers are inspired by the Fokker organ and its intriguing microtonal system.
This according to “Microtonaliteit van het Spaarne naar ’t IJ. Zestig jaar 31-toons orgel” by Cees van der Poel (Het orgel, 107/3  pp. 4–10). Above, Anton de Beer (1924–2000) plays the organ. Inset, the reassembled organ and a schematic of the keyboard (click to enlarge). You can hear excerpts from works performed on the Fokker organ here.
A black hole situated in the center of a galaxy amid a group of thousands of galaxies collectively called the Perseus Cluster (shown above) emits waves in a frequency equivalent to a B♭ 57 octaves below middle C, or one million, billion times lower than the lowest sound audible to the human ear. The Perseus black hole’s sound waves have a frequency of 10 million years.
This information, from an article published online by NASA, resonates with the philosophical concept often associated with Pythagoras and Johannes Kepler of Musica universalis or music of the spheres.