Echelon Spectroscopes and the Green Mercury Line

Abstract

IT is interesting, in reference to Prof. Nagaoka's letter in NATURE of April 23 (p. 581), to note that I exhibited photographs of the green mercury line, showing a number of new components, at the Leicester meeting of the British Association. I did not publish the number or position of the lines in the report, not being quite satisfied that some of the fainter ones might not be produced in the instrument, and I discovered later (NATURE, vol. lxxvii., pp. 198 and 222) that secondary effects, due to light reflected in the echelon, have to be taken into account. Since then Von Baeyer's measurements with a Lummer and Gehrcke spectroscope and Galitzin's echelon measurements have confirmed two of the lines that were new, and added confirmation to my values for the old ones. A doubt still remains, however, about some of the fainter lines, and as a comparison of the values given by different instruments is the most obvious way of confirming the true components and eliminating false ones, I give my results for comparison below.