C.= about 2200 deg.

F.) shows a few lines and flutings; when iron is heated in an electric arc (say, to 3500 deg.

C.= about 6300 deg.

F.) the spectrum shows some two thousand lines; at the higher temperature produced by the electric spark-discharge, the spectrum shows only a few lines.

As a guide to further investigation, we may provisionally infer from these facts that iron is changed at very high temperatures into substances simpler than itself.
Sir Norman Lockyer's study of the spectra of the light from stars has shown that the light from those stars which are presumably the hottest, judging by the general character of their spectra, reveals the presence of a very small number of chemical elements; and that the number of spectral lines, and, therefore, the number of elements, increases as we pass from the hottest to cooler stars.