but in addition a number of "enhanced lines," as Lockyer has chosen to call them. By reason of these latter, Lockyer assumes that the atom of iron (as well as of other elements) may consist of more elementary constituents at extremely high temperatures, and, if the cooler vapors could be removed from this hottest zone, the enhanced lines might stand alone for the elementary form of iron—as a proto-iron. Such conditions are said to be obtained in sun spots and our hottest stars. Whether the extremely high temperature alone is sufficient to produce the enhanced lines, or whether their origin lies in the enormously rapid changes of electric stress, can not be answered at present. In either case, there seems to be no doubt but that the atom of an element consists of yet smaller particles, which, with rise of the disintegrating forces, show a marked increase in their activities, and, owing to the similarity existing between these particles, give spectral lines of greater and greater simplicity.
When a group of lines in a spectrum has oscillation frequencies that obey a single formula we call this group a series. The simplest elements usually give three series, each of which consists of lines in doublets or triplets. The action of a strong magnetic field upon the series of an element's spectrum tends to decompose the series; each line is resolved into two or three lines (doublets or triplets) according as the light is viewed along or across the magnetic lines of force. This is called the Zeeman effect. Of the three components of motion of the particles, that one which lies in the direction of the lines of force with vibrations backwards and forwards can emit no light except when viewed at right angles to these lines of force. The other two motions at right angles to the lines of force suffer a retardation and acceleration, respectively, with the result that their oscillation frequencies are similarly affected and consequently two separate lines will be developed. These may be observed by themselves when the light is viewed along the lines of force or in conjunction with the original line—with position between these two—when the light is viewed across the magnetic field. The electro-magnetic composition of the atom therefore seems to be corroborated by these results.
As an analogy to this gradual disintegration of the atom under the great stress brought to bear upon it, and. further to show how the more complex molecules behave under the influence of temperature, we have only to examine the spectrum of a compound. Whatever compound is admitted into a flame, the characteristic spectrum of the molecule first makes its appearance. This consists not of lines, but of bands of varying widths. On further increase of temperature the decomposition of the compound molecule is attained, and the bands gradually give way to the characteristic lines of the elements concerned. With numerous compounds, for example, the metallic chlorides, this temperature is exceedingly low. Since the presence of spectral lines is un-
