Watch a Rubens tube in action. It uses fire to demonstrate sound waves.

Check out musician Moises Alves blowing a trumpet through a Rubens tube, which uses fire to provide a visual demonstration of sound waves. It's so cool! What's a Rubens tube? Science Facts provides an overview:

The Ruben's tube is a classic physics apparatus to show that sound waves are primarily pressure waves. It can be considered to be an older version of the oscilloscope and gives a visual demonstration of standing waves with the help of flames.

The Ruben's tube was invented in 1905, by a German physicist named Heinrich Rubens, born in 1865. The original device consisted of a four-meter-long section of a pipe with 200 holes of equal diameter placed uniformly along its length. The ends of the pipe were sealed, and an inflammable gas was pumped into it. Having no other way to escape, the gas came out of the holes and was then lit up to form flames of equal height.

Then, a loudspeaker was attached to one end of the device and sound was played into it when the heights of the flames changed depicting pressure differences set up within the tube due to the sound waves.

The video was posted on Moises Alves' YouTube channel, with this description:

Essa experiência chama-se Tubo de Rubens, cada nota tem um comprimento de onda e uma frequência e consequentemente quando as notas mudam, o tubo irá mostrar através do fogo. (This experiment is called a Rubens Tube, each note has a wavelength and a frequency and consequently when the notes change, the tube will show through the fire.)

For more from Alves, check out his Instagram page and YouTube channel. And to read more about the Rubens tube, check out the rest of the Science Facts article.