Chemical action always accompanies the sun’s light, but the analysis of the solar spectrum has partly disclosed the wonderful nature of the emanation. In the research, properties most important and unexpected have been discovered by Sir John Herschel, who imprints the stamp of genius on all he touches—his eloquent papers can alone convey an adequate idea of their value in opening a field of inquiry vast and untrodden. The following brief and imperfect account of his experiments is all that can be attempted here:— A certain degree of chemical energy is distributed through every part of the solar spectrum, and also to a considerable extent through the dark spaces at each extremity. This distribution does not depend on the refrangibility of the rays alone, but also on the nature of the rays themselves, and on the physical properties of the analyzing medium on which the rays are received, whose changes indicate and measure their action. The length of the photographic image of the _same_ solar spectrum varies with the physical qualities of the surface on which it is impressed. When the solar spectrum is received on paper prepared with bromide of silver, the chemical spectrum, as indicated merely by the length of the darkened part, includes within its limits the whole luminous spectrum, extending in one direction far beyond the extreme violet and lavender rays, and in the other down to the extremest red: with tartrate of silver the darkening occupies not only all the space under the most refrangible rays, but reaches much beyond the extreme red. On paper prepared with formobenzoate of silver the chemical spectrum is cut off at the orange rays, with phosphate of silver in the yellow, and with chloride of gold it terminates with the green, with carbonate of mercury it ends in the blue, and on paper prepared with the percyanide of gold, ammonia, and nitrate of silver, the darkening lies entirely beyond the visible spectrum at its most refrangible extremity, and is only half its length, whereas in some cases chemical action occupies a space more than twice the length of the luminous image.