Some circumstances that occurred during the analysis of the chemical spectrum seem to indicate an absorptive action in the sun’s atmosphere. The spectral image impressed on paper prepared with nitrate of silver and Rochelle salt commenced at, or very little below, the mean yellow ray, of a delicate lead colour; and when the action was arrested, such was the character of the whole photographic spectrum. But, when the light of the solar spectrum was allowed to continue its action, there was observed to come on suddenly a new and much more intense impression of darkness, confined in length to the blue and violet rays; and, what is most remarkable, confined also in breadth to the middle of the sun’s image, so far at least as to leave a border of the lead-coloured spectrum traceable, not only round the clear and well-defined convexity of the dark interior spectrum at the less refrangible end, but also laterally along both its edges; and this border was the more easily traced, and less liable to be mistaken, from its striking contrast of colour with the interior spectrum, the former being lead gray, the latter an extremely rich deep velvety brown. The less refrangible end of this interior brown spectrum presented a sharply terminated and regularly elliptical contour, the more refrangible a less decided one. “It may seem too hazardous,” Sir John continues, “to look for the cause of this very singular phenomenon in a real difference between the chemical agencies of those rays which issue from the central portion of the sun’s disc, and those which, emanating from its borders, have undergone the absorptive action of a much greater depth of its atmosphere; and yet I confess myself somewhat at a loss what other cause to assign for it. It must suffice, however, to have thrown out the hint, remarking only, that I have other, and I am disposed to think decisive, evidence of the existence of an absorptive solar atmosphere extending beyond the luminous one.” M. Arago observed that the rays from the centre of the sun have a greater photographic power than those from the edges, and the photographic images of the sun, taken on glass by M. Niepcé, were blood-red, much deeper in the centre, and on one occasion the image was surrounded by an auriol. Several circumstances concur in showing that there are influences also concerned in the transmission of the photographic action which have not yet been explained, as, for example, the influence which the time of the day exercises on the rapidity with which photographic impressions are made, the sun being much less effective two hours after passing the meridian than two hours before. There is also reason to suspect that the effect in some way depends on the latitude, since a much longer time is required to obtain an image under the bright skies of the tropics than in England; and it is even probable that there is a difference in the sun’s light in high