were aiming at the solution of the problem. Lieut. Herschel had suggested the use of coloured media admitting only such rays as the prominences emit. Mr. Lockyer was trying I know not what device of rotating or vibrating slits,

And one had aimed an arrow fair,

But sent it slackly from the string;
And one had pierced an outer ring
And one an inner here and there;
But last the master bowman, he
Had cleft the mark.

Fig. 75 represents the picture-rough, but instructive-of the first solar prominence ever seen when the Sun was not eclipsed.

So soon as the open-slit method had been suggested by Huggins many other observers adopted it. Mr. Lockyer, availing himself of the great dispersive power of the instrument Mr. Browning had made for bim, found that he could dispense with the use of coloured glasses. The prominences were rendered distinctly visible with

the open slit alone; and he could readily watch the changing figures of these mysterious objects. The accompanying drawings (figs. 76 and 77) exhibit two views of a wild and fantastic group of prominences, drawn by Mr. Lockyer, the second only ten minutes after the first was completed.

A group of solar prominences.-March 14, 1869, 11h. 5m. (Lockyer.) Dr. Zöllner, the eminent German photometrician, applied the same method in a systematic manner. Some of the pictures he has published are singularly interesting.

It is to be noticed, in the first place, that Dr. Zöllner

observed the same protuberance in three different colours, corresponding to the three lines of its spectrum. He found a material difference between the red and the blue image on the one hand and the yellow on the other. The latter is very intense only in close

proximity to the Sun's limb,* and corresponds there to the other images; but the more delicate details disappear at a greater distance. Zöllner suggests that

*It will be observed that Zöllner's results as regards the coloured images correspond with those obtained by Secchi in observing the coloured lines.

this may be explained on the hypothesis that the rays which give rise to the yellow image emanate from a gas having a greater specific gravity than hydrogen, and therefore existing at a lower level.'

The most interesting of Zöllner's drawings are exhibited in Plates IV. and V. It must be conceived by the reader that these views are only the red images. Zöllner saw perfectly similar blue images, and nearly similar orange-yellow images. The combination of the three produces the complete image as seen, during eclipse, with the telescope.

Respecting the several protuberances shown in Plate IV., he makes the following remarks:-'In fig. 1 we see an intensely luminous peak-shaped mass rising from the border of the Sun, above which is spread a cloud-like formation of less intensity. To the same type belong the protuberances of figs. 4 and 9. In fig. 4 it is remarkable that the surprisingly beautiful cumulus shape of the cloud was separated from the peak by a considerable distance. The cloud was exceedingly delicate, and even its finest details could be recognised. The separate cumuli of which it was composed appeared almost like dull luminous points.'

Fig. 2 was one of the most remarkable formations. I hardly believed my eyes,' says Zöllner, when I noticed in it the tongue-like motion of a flame. This motion was slower, however, compared with the size of the flame, than that of high towering flames at great conflagrations. The time required by such a wave in passing from the base to the apex was about two or