CHAP. II. point out that I did see 'willow-leaves' or 'rice-grains' pretty regularly shaped in the penumbra, and therefore might be expected to have seen them on the general surface of the sun had they been there. But I certainly saw nothing of the kind on the general surface of the sun. would seem indeed that there is a running down of the shape; for whereas on the sun the thing in debate is, according to my observation, a confused sort of circular mass, you get in the penumbra near the edge of the photosphere sometimes pointed, sometimes rounded, sometimes

of masses

truncated cloud masses, with a sharpened portion towards the umbra, and a very blunt portion towards the general solar surface. But if you observe similar masses which Different have traversed the penumbra, you find generally that they appearance are pointed at both ends, the point being sometimes rounded, after they sometimes truncated. Of course it would be extremely difficult-indeed it is an observation one can scarcely even hope to make-to watch a portion of photospheric matter coming in with a rush, as it sometimes does into the penumbra, then travelling through and changing its shape,

have crossed

penumbra.

and then finally setting sail and melting; but I venture to CHAP. II. think that, if that can be done, it will possibly be found that the confused circular mass which is seen on the general surface of the sun will be gradually drawn out in its journeying towards the umbra; and if you can get it to traverse over the umbra, you will find that it will look as much as possible like a willow-leaf."

Since this was communicated to the Astronomical Society Mr. Huggins has given his verdict very much to the same effect.

Now it has been satisfactorily proved, notably by a beautiful stereoscopic combination of them, suggested by Mr. De la Rue, that the faculæ are higher than the general surface of the sun; that is, where the clouds are highest they appear brightest-we see facula-because they extend high into the absorbing atmosphere; we know that on the bright surface of the sun rests an absorptive atmosphere, because the luminosity is remarkably less near the border, indicating that there is a greater thickness of atmosphere there which the light has to pass through before it reaches our eye. This point will be returned to in the sequel. The more minute features-the granules--are most probably the dome-like tops of smaller cloud masses, bright for the same reason that the faculæ are bright, but to a less degree; the fact also that the granules lengthen out as they approach the umbra of a spot is similar to the effect observed in the clouds in our own sky lengthened out when they are drawn into a current; while the admirable drawings by Secchi reproduced in the preceding pages show how plastic the photospheric matter was, to be thus torn and contorted.

But we shall see as we go on what a flood of light has been thrown on all these matters during the last few years.

Why we see

facule.

MR. CARRINGTON'S RESEARCHES ON

SOLAR SPOTS.

CHAP. III. SPOTS on the Sun! We can little realize nowadays all the hardihood required to make that assertion in Galileo's and Scheiner's time. Spots on that body which Aristotle the great master had declared to be the type of everything immutable and incorruptible; macula on the immaculate! spots on the last stronghold of the spotless! What wonder that even down to our time all the horror set agoing by that daring statement has not yet left off vibrating.

Newton's

query.

It is now more than 200 years ago since Scheiner, one of the first employers of the astronomical telescope, published his great book on the sun, in which these matters were first laboriously investigated. Since his time, especially in later years, many observers, and among them Schwabe, Wolf, Peters, and Laugier, have continued the work; but the wonder and astonishment which they call forth are not yet one whit diminished to such men as Herschel, and Helmholtz, and Thomson; nor are they the least part of that seemingly invincible mystery which surrounds the glorious sun, whose mighty power at last seems dawning upon us terricole.

Newton, in his times, was content to ask, "Are not the sun and fixed stars great earths vehemently hot?" and some 200 years later, in our own, Mr. Carrington is still driven to the question, with which we started this book,

"What is a Sun?" Now this question is a generic one, CHAP. III. embracing an infinitude of specific ones of more or less importance. Thus, for instance, we want to know something of its orbit-sustaining powers, and of the origin of these powers; looking at it, as a "great earth," we want to know when it will be as cool as ours is-as a star, if it be a variable one either in light or colour. Looking at it, again, as a sun, we want to know all its conditions, the secrets of its light and heat, of solar physics generally, and of the aforesaid spots, which, like straws on a stream, tell of the wondrous forces at work. And it is to learn something of these spots that Mr. Carrington has been Carring content to observe the sun every fine day for some seven years and a half, and to deduce the exact position of the spots observed. This he has done with a very definite object in view, and one which necessitated a forsaking of apparently all the most interesting kind of work connected with their telescopic appearance. He writes:-"The dis

tribution of radiative power, the position of the thermal equator, the numerical amount of illuminating power and its possible variations, the estimation even of the degree of energy exhibited in the production of spots, and many other features, were consciously left aside, and the subject before my mind reduced pretty much to tracing regularity in the distribution in the maculæ, detecting the true period of rotation of the body of the sun, and the determination of the systematic movements or currents of the surface, if such exist, in any definable manner."

The volume in which these researches appear, though a big book, is not the biggest we possess on this subject; but De Lambre tells us that the biggest-Scheiner's "Rosa Ursina "-should have rather consisted of 50 than 784 pages: so Mr. Carrington may take comfort.

Mr. Carrington,' distancing all previous inquirers in the

1 "Observations of the Spots on the Sun, from November 1853, to March 24, 1861, made at Redhill." By R. C. Carrington, F.R.S. Illustrated by 166 plates. Williams and Norgate.

D

ton's work

CHAP. III. perfection of his instrumental means, the methods of reduction employed, and the time he has given to the subject, presents us with values of the sun's elements, and of the time of its rotation, which it will be very difficult for future astronomers to improve upon.

Pheno

earth's

rotation.

In order that we may best communicate what he has mena of done, let us suppose a boundless ocean in which both earth and sun are half immersed. This will represent to us the plane of the ecliptic, or earth-plane. Let us further suppose both earth and sun to be rotating on their axes in a certain period of time, the axes being either upright or tipped down-i.e. inclined-to a certain extent in a certain direction.

Now, in the case of the earth we know exactly all these particulars. We know that our day results from, and is an exact measure of, our rotation; that our seasons are caused by a certain tipping down of the axis, and that the polestar marks for us, with sufficient accuracy for our present purpose, the exact amount and direction of this tipping down. The annexed woodcuts (Figs. 15-18) will give a good idea of these particulars in the case of our earth, and how its appearance changes in consequence as seen from the sun.

Equally, therefore, before we can properly define our sun as a member of our system, we must find out these particulars for it; we must know how it also is floating in our hypothetical ocean, whether at rest or perpendicularly, and if neither, then the length of its day, to speak in earthly language, and the position of its pole-star must be determined. But how is this to be accomplished? We need scarcely say that it is to the spots on the sun that we must look for the solution of these problems. Fortunately, the sun, when examined with a telescope, is not the equally illuminated disc it appears to be to the unaided vision, and the spots visible on its surface may be likened to straws which show us the rate and direction of a stream, for no sooner were they discovered than it was observed that they had motion across the sun.