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
Sound of a Woman a slowed down version, with a video showing her and others, slowly revealed to be without clothes, to express "raw emotions". Kiesza described "Sound of a Woman" as having grunge, rock, and folk influences in addition to her usual house or dance genre and that some songs on the album would be surprising to people. "Hideaway" was released on 11 April 2014 as Kiesza's debut single. Both the song and its accompanying music video have been met with general acclaim from contemporary music critics. "Hideaway" topped the UK Singles Chart upon release, selling over 136,000 copies in its first week,