A photograph of the spectrum of Tebbutt's comet, taken by him on the 24th of June 1881, showed radiations of shorter wave-lengths but identical source, and in addition, a percentage of reflected solar light marked as such by the presence of some well-known Fraunhofer lines.
Its purport is that glowing vapours similarly circumstanced absorb the identical radiations which they emit.
.It is true that within the body radiations must be stifled within a short distance of their source; none the less, they will determine a temperature gradient, falling from the centre to the borders, though for the most part falling very slowly, and we may ask what relative temperatures in different parts would maintain themselves if once established.
Since the only cause for these convection currents is the statical instability produced by radiation, and the rapid stifling of radiations within the body produces there a temperature gradient falling very slowly, they would be for the most part extremely slight.
The radiations from the sun must be considered in two parts, corresponding respectively to the continuous spectrum and the line-spectrum.