As to the movements of the constipated vapours forming spots, the spectroscope is also competent to supply information. The principle of the method by which it is procured will be explained farther on. Suffice it here to say that the transport, at any considerable velocity, to or from the eye of the gaseous material giving bright or dark lines, can be measured by the displacement of such lines from their previously known normal positions. In this way movements have been detected in or above spots of enormous rapidity, ranging up to 320 _miles per second_. But the result, so far, has been to negative the ascription to them of any systematic direction. Uprushes and downrushes are doubtless, as Father Cortie remarks,[465] "correlated phenomena in the production of a sun-spot"; but neither seem to predominate as part of its regular internal economy.
The same kind of spectroscopic evidence tells heavily against a theory of sun-spots started by Faye in 1872. He had been foremost in pointing out that the observations of Carrington and Spörer absolutely forbade the supposition that any phenomenon at all resembling our trade-winds exists in the sun. They showed, indeed, that beyond the parallels of 20° there is a general tendency in spots to a slow poleward displacement, while within that zone they incline to approach the equator; but their "proper movements" gave no evidence of uniformly flowing currents in latitude. The systematic drift of the photosphere is strictly a drift in longitude; its direction is everywhere parallel to the equator. This fact being once clearly recognised, the "solar tornado" hypothesis at once fell to pieces; but M. Faye[466] perceived another source of vorticose motion in the unequal rotating velocities of contiguous portions of the photosphere. The "pores" with which the whole surface of the sun is studded he took to be the smaller eddies resulting from these inequalities; the spots to be such eddies developed into whirlpools. It only needs to thrust a stick into a stream to produce the kind of effect designated. And it happens that the differences of angular movement adverted to attain a maximum just about the latitudes where spots are most frequent and conspicuous.