Note 124 — Chapter VIII

“Having noticed, one densely foggy day, that the disc of the sun was of a deep red colour, I directed my apparatus towards it. After ten seconds of exposure, I put the prepared plate in the mercury box, and I obtained a round image perfectly black;—the sun had produced no photogenic effect. In another experiment, I left the plate operating for twenty minutes; the sun had passed over a certain space of the plate, and there resulted an image seven or eight times the sun’s diameter in length; it was black throughout, so that it was evident, wherever the red disc of the sun had passed, not only was there a want of photogenic action, but the red rays had destroyed the effect produced previous to the sun’s passage. I repeated these experiments during several days successively, operating with a sun of different tints of red and yellow. These different tints produced nearly the same effect; wherever the sun had passed, there existed a black band.”—Mr. Claudet, On different properties of Solar Radiation, modified by coloured glass media, &c.: Phil. Trans. 1847. Part 2.