WEEKLY EVENING MEETING,

Friday, March 17, 1865.

MAJOR-GENERAL EDWARD SABINE, R.A. Pres. R.S. Vice-President, in the Chair.

BALFOUR STEWART, Esq. F.R.S.

On the latest Discoveries concerning the Sun's Surface.

It is well known that a distant body does not impress the eye with the idea of relief.

Thus distant mountains do not stand out like the nearer parts of a landscape, and the sun and moon appear only as flat discs.

But although neither to direct nor telescopic vision do these heavenly bodies appear spherical, yet it is possible to produce stereo scopic impressions by combining together two pictures of these bodies taken at different times.

This has been done by Mr. Warren De la Rue with great success, and this gentleman has produced numerous stereoscopic representations of our satellite, in which the general sphericity as well as the unevenness of surface come well out. He has also produced a more limited number of stereoscopic impressions of the sun; but our knowledge of the solar surface is only to a certain extent derived from these impressions, while it is to a greater extent derived from the careta! study of ordinary sun pictures.

The bounding luminous surface of the sun is termed his photosphere, and our subject may be divided with reference to the surface into three parts the first comprising the region above the photosphere; the second, the photosphere itself; and the third, the region beneath the photosphere.

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To commence with the region above the photosphere, it may be easily shown that this region contains a very dense atmosphere.

In the first place, according to a well-known law the dark lines in the solar spectrum denote the presence of certain substances in a state of vapour, and yet in a comparatively cold state, above the photosphere of the sun. These substances comprise among others sodium, mag nesium, iron, and nickel.

Again, the rim of the sun when viewed by the eye, but more conspicuously in photographs, appears less luminous than the central portions; and this would also appear to indicate the presence of an absorbing atmosphere of lower temperature than the photosphere, so that a ray of light from the border having to pass through a con

siderable thickness of this atmosphere would become diminished in brightness. (This was illustrated by a beautiful photograph taken by Mr. De la Rue.)

In the third place, the red flames and part of the corona which surround the sun during a total eclipse, reveal to us the presence of an extensive solar atmosphere.

It appeared to the Astronomer Royal and some others as probable that these bodies belong to the sun; but their connection with our luminary was put beyond doubt by Mr. De la Rue, who by means of the Kew heliograph was enabled to take photographic pictures of the sun at the total eclipse which happened in Spain in July, 1860.

(The photographs were exhibited; and it was seen that as the moon proceeded over the sun's disc, the red flames and part of the corona discovered themselves at that side which she had left, and were covered up by her disc at that side towards which she was approaching, thus showing that they belong to the sun.)

Another proof in favour of the idea that the red flames belong to the sun is derived from the nature of the light which they emit. This has great photographic power compared to its luminosity, so much so that one prominence was photographed by Mr. De la Rue, which was invisible to the naked eye. Now such rays can, as far we know, belong only to intensely heated gas, and such gas can only belong to the sun.

Next, with regard to the photosphere, or luminous envelope of the sun, this surface when viewed through powerful telescopes appears granulated or mottled. (Reference was here made to a diagram lent by the Rev. J. Howlett, and to a photograph by Mr. De la Rue.) But besides this, there is reason to believe that great defining as well as magnifying power discloses the fact that the whole photosphere of the sun is made up of detached bodies, interlacing one another and preserving a great amount of regularity, both in form and size. Mr. Jas. Nasmyth was the first to proclaim this curious fact--he called these bodies willow leaves; Mr. Stone has called them rice-grains; Padre Secchi, coups de pinceau. (Some photographs from drawings lent by Mr. Nasmyth were then exhibited.)

The faculæ belong to this part of the subject: they are detached portions of the photosphere which are much brighter than the region around them; but this difference in brightness is chiefly apparent near the sun's limb. The reason of this is believed to be, that they are portions of the sun's photosphere thrown up into the higher regions of the atmosphere, by which means they are enabled to escape a great part of the absorbing effect of this atmosphere which is particularly strong near the border; while near the centre the absorption is not great, so that they do not gain much by escaping it.

The idea that faculæ are elevated has been confirmed by a stereoscopic impression of a sun-spot and some faculæ taken by Mr. De la Rue, in which the spot appears to be a hollow while the faculæ appear as elevated ridges.

It should also be remarked, that faculæ retain the same appearance often for a considerable time, sometimes even for days together, so that they are clearly not composed of heavy matter, but are rather of the nature of a cloud.

The phenomena of the third region, or that beneath the photosphere, may be embraced in one word, "sun-spots." These consist of an umbra, or central darkness, surrounded by a less dark penumbra. Mr. Dawes has discovered in some spots even a deeper darkness in the centre of the umbra.

Now if that theory of spots be correct which supposes that they are cavities of which the umbra forms the bottom, while the penumbra constitutes the sloping sides, then the umbra ought apparently to encroach on that side of the penumbra which is nearest the visual centre of the disc.

Prof. Alex. Wilson, of the University of Glasgow, was the first to remark that spots really behaved in this manner, and his observations have been abundantly confirmed by the Kew photographs. (One of these was exhibited.)

It therefore follows, that the umbra of a spot is at a lower level than the penumbra ; and since luminous ridges, and sometimes detached portions of luminous matter, cross over spots, it must be concluded that the whole phenomenon is below the surface.

In the next place, spots are the means of exhibiting to us the rotation of our luminary. If we turn to the south and view the sun spots always cross the disc from east to west, that is to say from left to right. (The apparent path of a spot at different seasons was here traced on a diagram, constructed and lent by Rev. F. Howlett; and it was remarked that when allowance is made for the inclination of the earth's axis, the path is really the same at different seasons.)

Besides the apparent motion due to rotation of the sun, spots have also a proper motion of their own, which was discovered by Mr. Carrington. This motion is also from left to right; those near the solar equator moving fastest. Mr. Carrington also remarked that spots confine themselves to the equatorial regions of the sun.

Hofrath Schwabe, of Dessau, has remarked that spots have a period of maximum and minimum nearly every ten years, and General Sabine has found that the year of maximum sun-spots is at the same time that of greatest disturbance of the earth's magnetism.

Finally, the behaviour of sun-spots appears to some extent to be influenced by the planet Venus, in such a manner that when a spot comes round by rotation to the ecliptical neighbourhood of this planet, it has a tendency to dissolve; and on the other hand, as the sun's surface recedes from this planet, it has a tendency to break out into spots.

[B. S.]

WEEKLY EVENING MEETING,

Friday, March 24, 1865.

JOHN PETER GASSIOT, Esq. F.R.S. in the Chair.

PROFESSOR WESTMACOTT, R.A. F.R.S.

On Art-Education, and how Works of Art should be viewed.

THE speaker felt that it would be expected of him to discourse on Art, and especially on that Art to which he had given many years' attention. As, however, it would be impossible to condense, within the short time allowed, any sufficient history of Sculpture, or a clear exposition of the various characteristics of the Art during the long period of its ancient and modern practice, or to enter thoroughly upon merely technical matter, as if he were addressing Art-students, he proposed to take a view of the subject which should interest a general and unprofessional audience; namely, in what way works of Art should be considered by the public, so as to afford the largest amount of gratification and profit.

The interest now taken in Art is a fair ground for offering some remarks on the best way of directing the public intelligence in this important field. Museums, collections, exhibitions, abound all over the country, and the large numbers of visitors to these show beyond dispute how willing people are to find amusement in such displays. The statistics on this subject would be very curious; but, beyond this, they would suggest serious reflection whether this class of entertainment might not be made a means of greatly benefiting the moral and intellectual condition of the people. It is well known that many thousands visit, in the course of every week in the year, the two great public museums of Art in London; while during the ten or twelve weeks only to which the exhibition of the Royal Academy is, of necessity, confined, and when 1s. is paid for admission, such large numbers attend that, last season, considerably above £12,000 was taken at the doors.

Now, a question arises, whether, and how far, this general interest felt in Art has had any beneficial influence on the public Taste. The answer scarcely can be considered satisfactory. As a nation, we cannot be said to exhibit this quality in any eminent degree; and the inquiry naturally suggests itself, why, with this large supply of Art and this disposition to look at Art-productions, should this inferiority exist?

Chiefly, then, if not entirely, it may be attributed to the absence of any education in the principles of Art. It is not recognized, even in

our universities, as a part of polite training; so that usually, even among the superior classes, the most crude notions prevail upon the theory and principles of design; while all the higher aims and objects of Art are utterly ignored.

The value of any production, whether of High Art or Literature, and the measure of enjoyment to be derived from it, must be in the ratio of a person's capacity or power to understand it. How is this power to be acquired?

That there is no indisposition, generally, in the public to be better informed is shown by the readiness with which they seek direction where they fancy it may be obtained. In public galleries an eager interest is shown to listen to any chance explanations that may be going on. On visiting exhibitions of pictures, people seek direction in the same way, or they are found procuring marked catalogues from some one or other whose judgment they may think superior to their own; a proof, at least, of willingness to be assisted, though the advantage gained may sometimes be questioned. They may be told what to look at; but they are not taught how to see it. They are without any guide to explain to them the broad principles of Art; in what its value really consists; and what are its claims to consideration as a means of expressing and developing the Beautiful. They simply find particular works pointed out for examination; but no reasons are asked or given for their being thought good, or condemned as bad; and the critic and guide may himself be totally incompetent, if not, as is too often the case, biassed by favouritism or prejudice.

It is precisely here that the want of a sound education in the theory and the principles of Art, as distinct from the merely technical, is seen. The public is thrown upon individual, and perhaps extremely one-sided, opinion, from which it takes its impressions, instead of having the power of forming for itself a judgment based upon a safe foundation.

Amongst the errors to which an uneducated public is prone in estimating works of Art is the fancy that mere imitation constitutes excellence. It has its own very great merit. As a mechanical accomplishment it, no doubt, ranks, and should rank very high; and an artist cannot be too diligent in mastering this most important element of practice, as his language of expression. But it never should be forgotten that imitation is only a means to an end; and not the end, as many seem to think it. It is what words are to the orator:the language by which ideas are to be conveyed. This erroneous opinion, as to the extreme merit of mere imitation, per se, has led to much degradation of Art. Instead of making Art the medium of expressing the great and the good in forms of beauty-as all the great artists of the great periods of Art have done-modern Art is frequently found illustrating the most ordinary and commonplace subjects, selected, as it would seem, simply with the view of enabling the artist to show his skill in the minute and elaborate imitation of what very often are but mean and undignified details. Art should aspire to raise men's