WITH regard to Mr. Butler's letter on this subject (NATURE, vol. lxxxviii., No. 2199, p. 244), I may say that I was unaware that Hα had been photographed in the “flash” spectrum in former total solar eclipses. As I have also been, so far, unsuccessful in my search in the preliminary reports of the eclipse observers of 1893 and 1898, in the Proceedings and in the Philosophical Transactions of the Royal Society, in finding any specific mention of H, would Mr. Butler kindly supply the needed references? I may add that in the photograph taken by Father Pigot under my direction in the last eclipse, H does not appear as an isolated arc, such as might be recorded on an isochromatic plate, but as the strongest impression crossing a continuous band which extends from H well into the ultra-violet. A modification of my original statement in this sense might meet Mr. Butler's criticism.