Note 89 — Chapter VII

Sir John Herschel, in his paper On the Chemical Action of the Rays of the Solar Spectrum on Preparations of Silver, remarks that, “it may seem too hazardous 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 (which will find its place elsewhere) of the existence of an absorptive solar atmosphere, extending beyond the luminous one. The breadth of the border, I should observe, is small, not exceeding 0·5 or 1/7 part of the sun’s radius, and this, from the circumstances of the experiment, must necessarily err in excess.”—Philosophical Transactions, 1840.