IV. Note on the reduction of the observations of the spectra of 100 sun-spots observed at Kensington

In anticipation of a more detailed communication I beg to lay before the Royal Society some of the results of the reduction of six most widened lines between F andb seen in the spectra of 100 sun-spots, observed at Kensington between November 12th, 1879, and September 29th, 1880, limiting my remarks solely to the spectrum of iron. In the accompanying map, the Fraunhofer lines agreeing in position with the iron lines given by Ångström and Thalén are entered in the horizon headed “Sun,” in the next are plotted the lines assigned to iron by Ångström, who used the electric arc in his experiments. In the next horizon are entered the iron lines given by Thalén, who employed the induction coil in his experiments. In these three horizons the lengths of the lines represent their intensities.