Page:On Radiation.djvu/63

 other words, reduce it to the radiant form. By this process, which has been called Dynamic Radiation, the radiative power of both vapours and gases has been determined, and the reciprocity of their radiation and absorption proved. In the excellent researches of Leslie, De la Provostaye and Desains, and Mr Balfour Stewart, the reciprocity of radiation and absorption in the case of solid bodies has been variously illustrated; while the labours, theoretical and experimental, of Kirchhoff have given this subject a wonderful expansion, and enriched it by applications of the highest kind. To their results are now to be added the foregoing, whereby a vast class of bodies hitherto thought inaccessible to experiment, are proved to exhibit the duality of radiation and absorption, the influence on both of chemical combination being exhibited in the most decisive and extraordinary way.