The Boundary Layer

Emil Gilels’ performance of Domenico Scarlatti’s Sonata K533


The Boundary Layer refers to an actual boundary layer. I learned about boundary layers from NASA educational materials about basic aerodynamics:

As an object moves through a fluid, or as a fluid moves past an object, the molecules of the fluid near the object are disturbed and move around the object. Aerodynamic forces are generated between the fluid and the object. The magnitude of these forces depend on the shape of the object, the speed of the object, the mass of the fluid going by the object and on two other important properties of the fluid; the viscosity, or stickiness, and the compressibility, or springiness, of the fluid…
Aerodynamic forces depend in a complex way on the viscosity of the fluid. As the fluid moves past the object, the molecules right next to the surface stick to the surface. The molecules just above the surface are slowed down in their collisions with the molecules sticking to the surface. These molecules in turn slow down the flow just above them. The farther one moves away from the surface, the fewer the collisions affected by the object surface. This creates a thin layer of fluid near the surface in which the velocity changes from zero at the surface to the free stream value away from the surface. Engineers call this layer the boundary layer because it occurs on the boundary of the fluid.

I have often thought about how music arises from the world. There is always a time when a musical composition is first written down or communicated to another person. So where does the music come from, and why does it happen? I am not at all familiar with aerodynamics, other than the basic, elementary physics behind them which I can read about on the NASA website. But the idea of there being a layer defined when fluid moves past an object was too compelling. The concept of a boundary layer seems pretty significant in music and music performance.
The text on this painting refers to a W.B. Yeats poem, The Host of the Air. The painting begins with the last section of the Sonata.