Since the "wires" are stretched precisely in the focus, where the principal image of the sun is formed, and move in it, they, and the features of the surface, form one picture, as magnified by the eye lens, so that they appear as if moving about on the sun itself. We can first set them far enough apart, for instance, to take in the whole of a spot, and then by bringing them together measure its apparent diameter, in ten thousandths of an inch. Then, measuring the diameter of the whole sun, we have evidently the proportion that one bears to the other, and hence the means of easily calculating the real size. A powerful piece of clockwork, attached to the equatorial, keeps it slowly rotating on its axis, at the same angular rate as that with which the sun moves in the sky, so that any spot or other object there will seem to stay fixed with relation to the "wires," if we choose, all day long. The picture of "wires," spots, and all, may be projected on a screen if desired; and [Fig. 11] shows the field of view, with the micrometer wires lying across a "spot," so seen on the 6th of March, 1873. Part of a cambric needle with the end of a fine thread is represented also as being projected on the screen along with the "wires" to give a better idea of the delicacy of the latter.
Now we may measure, if we please, the size of one of those bright objects, which have just been spoken of as being countable by hundreds of thousands. These "little things" are then seen to be really of considerable size, measuring from one to three seconds of arc, so that (a second of arc here being over 400 miles) the average surface of each individual of these myriads is found to be considerably larger than Great Britain. Near the edge of the disk, under favorable circumstances, they appear to rise up through the obscuring atmosphere, which darkens the limb, and gathered here and there in groups of hundreds, to form the white cloudlike patches (faculæ), which may sometimes be seen even with a spy-glass—"something in the sun brighter than the sun itself," to employ the expression by which Huyghens described them nearly two hundred years ago. They are too minute and delicate objects to be rendered at all in our engraving; but this is true also of much of the detail to be seen at times in the spots themselves. The wood cuts make no pretense to do more than give an outline of the more prominent features, of which we are now about to speak. The wonderful beauty of some of their details must be taken on trust, from the writer's imperfect description of what no pencil has ever yet rendered and what the photograph has not yet seized.
Bearing this in mind, let us now suppose that while using the polarizing eyepiece on the part of the spot distinguished by the little circle, we have one of those rare opportunities when we can, by the temporary steadiness of our tremulous atmosphere, use the higher powers of the telescope and magnify the little circle till it appears as in [Fig. 12]. We have now nearly the same view as if we were brought close to the surface of the sun, and suspended over this part of the spot. All the faint outer shade, seen in the smaller views (the penumbra) is seen to be made up of long white filaments, twisted into curious ropelike forms, while the central part is like a great flame, ending in fiery spires. Over these hang what look like clouds, such as we sometimes see in our highest sky, but more transparent than the finest lace vail would be, and having not the "fleecy" look of our clouds, but the appearance of being filled with almost infinitely delicate threads of light. Perhaps the best idea of what is so hard to describe, because so unlike anything on earth, is got by supposing ourselves to look through successive vails of white lace, filled with flower-like patterns, at some great body of white flame beyond, while between the spires of the flame and separating it from the border are depths of shade passing into blackness. With all this, there is something crystalline about the appearance, which it is hard to render an idea of—frost-figures on a window pane may help us as an image, though imperfect. In fact the intense whiteness of everything is oddly suggestive of something very cold, rather than very hot, as we know it really. I have had much the same impression when looking into the open mouth of a puddling furnace at the lumps of pure white iron, swimming half-melted in the grayer fluid about them. Here, however, the temperature leaves nothing solid, nothing liquid even; the iron and other metals of which we know these spot-forms do in part at least consist are turned into vapor by the inconceivable heat, and everything we are looking at consists probably of clouds of such vapor; for it is fluctuating and changing from one form into another while we look on. Forms as evanescent almost as those of sunset clouds, and far more beautiful in everything but color, are shifting before us, and here and there we see, or think we see, in the sweep of their curves beyond, evidences of mighty whirlwinds (greater by far than the largest terrestrial cyclone) at work. While we are looking, and trying to make the most of every moment, our atmosphere grows tremulous again, the shapes get confused, there is nothing left distinct but such coarser features as our engraving shows, and the wonderful sight is over. When we consider that this little portion of the spot we have been looking at is larger than the North and South American continents together, and that we could yet see its parts change from minute to minute, it must be evident that the actual motion must have been rapid almost beyond conception—a speed of from 20 to 50 miles a second being commonly observed and sometimes exceeded. (A cannon ball moves less than ¼ of a mile per second.) I have seen a portion of the photosphere, or bright general surface of the sun, drawn into a spot, much as any floating thing would be drawn into a whirlpool, and then, though it occupied by measurement over 3,000,000 miles in area, completely break up and change so as to be unrecognizable in less than twenty minutes.
When we come to discuss the subject of the sun's heat, we shall find that the temperature of a blast furnace or of the oxyhydrogen blowpipe is low compared with that which obtains all over such a vast region, and remembering this, it is evident that its disappearance is a cataclysm of which the most tremendous volcanic outburst here gives no conception. We cannot, by any terrestrial comparison, describe it, for we have no comparison for it in human experience. If we try to picture such an effect on the earth, we may say in another's words that these solar whirlwinds are such as, "coming down upon us from the north, would in thirty seconds after they had crossed the St. Lawrence be in the Gulf of Mexico, carrying with them the whole surface of the continent in a mass, not simply of ruin, but of glowing vapor, in which the vapors arising from the dissolution of the materials composing the cities of Boston, New York, and Chicago would be mixed in a single indistinguishable cloud."
These vast cavities then in the sun we call spots are not solid things, and not properly to be compared even to masses of slag or scoria swimming on a molten surface. They are rather rents in that bright cloud surface of the sun which we call the photosphere, and through which we look down to lower regions. Their shape may be very rudely likened to a funnel with sides at first slowly sloping (the penumbra), and then suddenly going down into the central darkness (the umbra). This central darkness has itself gradations of shade, and cloud forms may be seen there obscurely glowing with a reddish tinge far down its depths, but we never see to any solid bottom, and the hypothesis of a habitable sun far within the hot surface, suggested by Sir William Herschel, is now utterly abandoned. We are able now to explain in part that mysterious feature in the sun's rotation before insisted on, for if the sun be not a solid or a liquid, but a mass of glowing vapor, it is evidently possible that one part of it may turn faster than another. Why it so turns, we repeat, no one knows, but the fact that it does is now seen to bear the strongest testimony to the probable gaseous form of the sun throughout its mass—at any rate, to the gaseous or vaporous nature of everything we see. We must not forget, however, that under such enormous temperature and pressure as prevail there the conditions may be—in fact, must be—very different from any familiar to us here, so that when we speak of "clouds," and use like expressions, we are to be understood as implying rather an analogy than an exact resemblance.