A recent number of Poggendorff's “Annalen” contains a short but interesting paper by Christiansen, of Copenhagen, in which he states that a hollow prism filled with the alcoholic solution of fuchsine produces a highly anomalous spectrum, which, instead of proceeding regularly from the red to the violet like the ordinary solar spectrum, stops at a certain point, returns backward, then stops again and resumes a direct course to the end. This paper by Christiansen, kindly pointed out to me by Professor Tait, recalls to my memory an experiment which I formerly made more than thirty years ago, and which, with the permission of the Society, I will briefly describe, premising, however, that I write from memory, and without access at present to the original paper which I believe I have still preserved.