I. The photographic spectrum of electrolytic iron

This investigation is an extension of the author’s earlier researches on the spectrum of iron, and supplements the important paper published by Thalén in 1884. Since the work was commenced, two other papers on the spectrum of iron have been published, one by Professors Kayser and Runge, of the Hanover Technical High School, and the other by Mr. F. McClean. In the former, the arc spectrum of ordinary commercial iron was in question. The wave-lengths were determined by micrometric measures, a number of standard lines being used to construct the interpolation curves. Mr. McClean’s paper consists of a series of photographic comparisons of the spark spectrum of iron and the solar spectrum.