Kirchhoff's law of thermal radiation rarefied material such as air, or transparent material, through which observations can be made. The interface is not a material body and can neither emit nor absorb. It is a mathematical surface belonging jointly to the two media that touch it. It is the site of refraction of radiation that penetrates it and of reflection of radiation that does not. As such it obeys the Helmholtz reciprocity principle. The opaque body is considered to have a material interior that absorbs all and scatters or transmits none of the radiation that reaches it through refraction at the interface. In this sense
A Sound Garden A Sound Garden A Sound Garden is one of six outdoor public art works on the National Oceanic and Atmospheric Administration (NOAA) campus that lies adjacent to the Warren G. Magnuson Park on the northwestern shore of Lake Washington in Seattle, Washington. The Seattle Arts Commission guided the jury selection headed by Sadao James Hilario, Engineer-in-charge of the GSA Art in Architecture Program for the NOAA Project, and the jury chose five artists from a pool of more than 250. Designed and built by sculptor Douglas Hollis from 1982–83, "A Sound Garden" is a sculptural group composed of 12 21