and low latitudes, because an image of the solar spectrum, obtained on a Daguerreotype plate in Virginia, by Dr. Draper, differed from a spectral image obtained by Mr. Hunt on a similar plate in England. The inactive spaces discovered in the photographic spectrum by M. E. Becquerel, similar to those in the luminous spectrum, and coinciding with them, is also a phenomenon of which no explanation has yet been given; possibly the chemical rays may be absorbed by the atmosphere with those of light. Although chemical action extends over the whole luminous spectrum, and much beyond it, in gradations of more or less intensity, it is found by careful investigation to be by no means continuous; numerous inactive lines cross it, coinciding with those in the luminous image as far as it extends; besides, a very great number exist in the portions that are obscure, and which overlap the visible part. There are three extraspectral lines beyond the red, and some strongly marked groups on the obscure part beyond the violet; but the whole number of those inactive lines, especially in the dark spaces, is so great that it is impossible to count them. Notwithstanding this coincidence in the inactive lines of the two spectra, photographic energy is independent of both light and heat, since it exerts the most powerful influence in those rays where they are least, and also in spaces where neither sensibly exist; but the transmission of the sun’s light through coloured media makes that independence quite evident. Heat and light pass abundantly through yellow glass, or a solution of chromate of potash; but the greater part of the chemical rays are excluded, and chlorine gas diluted with common air, though highly pervious to the luminous and calorific principles, has the same effect. Sir John Herschel found that a slight degree of yellow London fog had a similar effect with that of pale yellow media: he also remarked that a weak solution of azolitmine in potash, which admits a great quantity of green light, excludes chemical action; and some years ago the author, while making experiments on the transmission of chemical rays, observed that green glass, coloured by oxide of copper about the 20th of an inch thick, excludes the photographic rays; and, as M. Melloni has shown that substance to be impervious to the most refrangible calorific rays, it has the property of excluding the whole of the most refrangible part of the solar spectrum, visible and invisible. Green mica, if not too thin, has also the same effect, whereas amethyst, deep blue, and violet-coloured glasses, though they transmit a very little light, allow the chemical rays to pass freely. Thus light and photographic energy may be regarded as distinct parts of the solar beam, and both being propagated by vibrations of the etherial medium they are merely motion. Excellent images have been obtained of the moon in its different phases by Professor Secchi, at Rome;