He made important researches in photochemistry, made portrait photography possible by his improvements (1839) on Daguerre's process, and published a Text-book on Chemistry (1846), Text-book on Natural Philosophy (1847), Textbook on Physiology (1866), and Scientific Memoirs (1878) on radiant energy.
Much as the decade from 1880 to 1890 abounded with investigations on the reactions of bacteria to heat, so the following decade was remarkable for discoveries regarding the effects of other forms of radiant energy.
The investigations both of Balfour Stewart and of Kirchhoff are based on the idea of an enclosure at uniform temperature and the general results of the reasoning centre in the conclusion that the introduction of any body at the same temperature as the enclosure can make no difference to the streams of radiant energy which we imagine to traverse the enclosure.
But when light is transmitted through a material medium, it always suffers some loss, the light energy being absorbed by the medium, that is, converted partially or wholly into other forms of energy such as heat, a portion of which transformed energy may be re-emitted as radiant energy of a lower frequency.
It also shows that the black body emits at a peak wavelength, at which most of the radiant energy is emits at a peak wavelength, at which most of the radiant energy is emitted.
