
A generic example of a boundary surface around a shape.

A generic example of a boundary surface around a shape.

In thermodynamics, a boundary surface is the term used by American mathematical physicist William Sidis in 1920 to describe the surface region or boundary of space around a black hole viewed in terms of it being thermodynamic system or working body. [1]

References
1. Sidis, William J. (1920). The Animate and the Inanimate (ch. 8: Stellar Hypothesis). Publisher: R.G. Badger, 1925.