SOLAR WONDERS.
ASTRONOMERS have been revealing so many wonders in the vast globe which rules the planetary scheme, that we cannot yet hope to see the startling results of their researches co-ordinated into a consistent whole. On every hand new marvels are being brought to light. At one time, Mr. Lockyer surprises us by exhibiting the amazing velocities with which the solar storms rage across the blazing surface of our luminary. At another, the energetic astronomer who presides over the Roman Observatory tells us of water within the fierce tumult of the solar spots. The Kew observers track the strange influences of the planets on the solar atmosphere, watching not only the great tide of spots which sweeps in the ten-year period over the solar storm-zones, and then leaves our sun clear from speck or stain, but also the ripples of spot-formation which come in shorter periods, and seem inextricably blended to ordinary observers with the great periodic disturbances. Lastly, Lockyer, Huggins, Ziillner, and Secchi describe the magic changes of form which pass over tongues of flame, projecting thousands of miles from the solar surface.
We have before us as we write a series of coloured prominence- pictures taken by Dr. &inner, the eminent photometrician. It is impossible to contemplate these strange figures without a sense of the magnificence of the problem which the sun presents to astronomers. Here are vast entities,— flames, if we will, but flames unlike all those with which we are familiar. And these vast tongues of fire assume forms which speak to us at once of the action of forces of the utmost violence and intensity. The very aspect of these objects at once teaches this, but it is the rapid changes of place and of figure to which the spots are subjected that are most significant on this point. Here is a vast cone-shaped flame, with a mushroom-shaped head of enormous proportions, the whole object standing 16,000 or 17,000 miles from the sun's surface. In the cone figure we see the uprush of lately imprisoned gases, in the outspreading head the sudden diminution of pressure as these gases reach the rarer upper atmosphere. But turn from this object to a series of six pictures placed beside it, and we see the solar forces in action. First, there is a vast flame, some 18,000 miles high, bowed towards the right, as though some fierce wind were blowing upon it. It extends in this direction some four or five thousand miles. The next picture represents the same object ten minutes later. The figure of the prominence has wholly changed. It is now a globe- shaped mass, standing on a narrow stalk of light above a row of flame-hillocks. It is bowed towards the left, so that in those short minutes the whole mass of the flame has swept thousands of miles away from its former position. Only two minutes later, and again a complete change of appearance. The stalk and the flame-hillocks have vanished, and the globe-shaped mass has become elongated. Three minutes later, the shape of the pro- minence has altered so completely that one can hardly recognize it for the same. The stalk is again visible, but the upper mass is bowed down on the right so that the whole figure resembles a gigantic A, without the cross-bar, and with the down-stroke abnormally thick. This great A. is some twenty thousand miles in height, and the whole mass of our earth might be bowled between its legs without touching them! Four minutes pass, and again the figure has changed. The flame-hillocks reappear, the down- stroke of the A begins to raise itself from the sun's surface. Lastly, after yet another interval of four minutes, the figure of the promi- nence has lost all resemblance to an A, and may now be likened to a camel's head looking towards the right. The whole series of changes has occupied but twenty-three minutes, yet the flame exceeded our earth in volume tenfold at the least. But Mr_ Lockyerhas recorded an instance of a yet more marvellous nature- A vast prominence extending seventy or eighty thousand miles from the sun's surface vanished altogether in ten minutes. The very way in which Zollner's drawings were taken savours of the marvellous. We have spoken of them as coloured. They are ruby-red, and so the prominences appeared to the astronomer. The real light of the prominences is not ruby-red, however, but rose- coloured, with faint indications of pink, or even bluish tints. The fact is, that by the new method of observation the image of a pro- minence is formed by only a certain part of its light. We may say that out of several coloured images of the same prominence the astronomer selects one only for examination.
The explanation of this is worth considering, as it involves the essence of the method by which the prominences are seen at all. When we analyze light with a simple prism as Newton did, we get instead of a round spot of white—that is, mixed light—a row of overlapping spots of different colour. It wakonly when, instead of a round spot, a fine line of white light was analyzed, that one- could detect the absence of images of this line along certain. parts of the rainbow-coloured streak,—in other words, it was thus only that the dark lines of the spectrum could be seen. And it was to see these lines more clearly that the slit of the spectroscope was made so narrow and the rainbow-spectrum made so long by spec- troscopists. But the observers of the prominences go back to the old method. If they used a narrow slit, a narrow strip of the prominence would alone form its spectrum, which would consist of a few bright lines. But by having a wide alit the whole promi- nence forms its spectrum, which consists of a few bright pictures- of the prominences. There is a green picture corresponding to the bright spectral line called F, a red picture corresponding to the bright spectral line called C, and so on. If the whole set of pictures were formed at once we could see none of them, for there: would be side by side with them the blazing solar spectrum which, would obliterate them altogether, just as in ordinary telescopie observation the bright sunlight blots out the prominences from view.
But if the observer uses such a battery of prisms that the solar- spectrum would be very long indeed, and if he admits to view. only that part of the spectrum oppositewhich one of the prominence -- images exists, he can then see that image quite distinctly, for the- neighbouring part of the solar spectrum is so reduced in splendour that it no longer obliterates the prominence-figure.
In this way, then, the observer selects one or other of the pictures of a prominence, either the red or the green picture, to. examine. And strangely enough, it is by no means certain that the two pictures are alike. Rather it is highly probable that they are different, though we have not space here either to indicate the reasons for believing this, or to explain the significance of the circumstance should it eventually be established.
It seems to us that when we consider the real dimensions of the solar globe, we appreciate more fully the wonderful nature of those processes of action indicated by recent researches, than when we
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