According to the first view, the true atmosphere of the sun is limited by the chromosphere, and the constituents of that atmosphere consist essentially of the vapours of the chemical elements recognized on the earth. It will be seen that on this view the corona and the equatorial extension observed occasionally are merely solar appendages. In the other view the atmosphere of the sun is extended to the confines of the corona, the temperature naturally increasing as we descend; and it is held that towards the photosphere the temperature is so high that the chemical elements are dissociated into finer forms of matter, so that descending vapours get more simple, ascending vapours get more complex, and it is only in the cooler regions of the atmosphere that vapours resembling those of our terrestrial elements can exist, while near the confines of the corona these vapours give place to solid particles and masses. Broadly stated, these divergent views have arisen from the application of two distinct methods of inquiry. In one method, light coming from every portion of the sun, and reflected, let us say, by a cloud into the spectroscope, gives us a spectrum full of absorption lines, and these lines are practically constant from year to year. In the other method, each minute portion of the solar economy has been examined bit by bit, and thus we have the spectrum of the spots, the spectrum of the prominences, the spectrum of the chromosphere, the spectrum of the corona. All these spectra vary enormously, not only among themselves, but from year to year; and, when we consider merely the spots and prominences, we may say that they vary from spot to spot and from prominence to prominence.

It will be obvious that the true mean density of the sun cannot be the same on the two hypotheses to which we have referred. If the atmosphere is practically limited by the photosphere, it has been found that the density of the sun is L444, water being taken as unity. If we include the corona in the sun’s atmosphere, and assume that its height is half a million of miles above the photosphere, then the volume of the sun is ten times that bounded by the photosphere, and the density is reduced to a tenth of the value given above.

We next proceed to discuss the chemical results obtained by the first method of inquiry to which reference has been made. For these results we are of course dependent upon comparisons of the lines given by various incandescent vapours with the Fraunhofer lines seen in the ordinary spectrum of the sun. If by such means complete evidence is afforded of the existence of one of our chemical elements in the sun, it is obvious that no information is given as to its precise locality; further, if the high temperatures used in our laboratories to produce a spectrum should break up the molecules of the vapours as known to the chemist into finer ones, and if the temperature of the sun were to do the same, there would still be a considerable similarity between the solar and the terrestrial spectrum of any one substance.

The first (A) of the following tables gives the substances present in the sun’s atmosphere according to (1) Kirchhoff, and (2) Angstrom and Thalén.

Table A. [table]

A subsequent method of inquiry, which was capable of tracing merely a small quantity, gave the additional substances shown in Table B. Table B.

Elements whose Longest Lines coincide with Fraunhofer Lines. [table]

When we come to bring the chemical evidence together which has been acquired by the examination of separate parts of the solar economy, we find, as has been already hinted, that the apparent similarity in chemical structure suggested by the foregoing tables entirely breaks down. Not only is the chemical nature of each separate solar phenomenon different from that of any other, but the facts of observation are in all cases entirely new and strange, so that very little light is obtained towards the understanding of them from ordinary laboratory work.

We will consider the chemistry of the chief solar features in order.

Chemistry of the Constituent Parts.

The spectrum of the spots differs from that of the ordinary surface of the sun chiefly by the widening of certain of the Fraunhofer lines in the spot spectrum,— some being excessively widened. The lines which are most widened change from spot to spot and from year to year. The most extensive sun-spot observations of this nature have been carried on in Kensington, and the conclusions derived from 700 observations on spots between 1879 and 1885 are as follows :—

(1) The spot spectra are very unlike the ordinary spectrum of the sun: some Fraunhofer lines are omitted; new lines appear; and the intensities of the old lines are changed.

(2) Only very few lines, comparatively speaking, of each chemical element, even of those which have many among the Fraunhofer lines, were seen to be most widened. It was as if on a piano only a few notes were played over and over again, always producing a different tune.

(3) An immense variation from spot to spot was observed between the most widened lines seen in the first hundred observations. Change of quality or density will not account for this variation. To investigate this point the individual observations of lines seen in the spectrum of iron were plotted out on strips of paper, and an attempt made to arrange them in order, but without success, for, even when the observations were divided into six groups, about half of them were left outstanding.

(4) If we consider the lines of any one substance, there is as much inversion between them as between the lines of any two metals. By the term “inversion” is meant that of any three lines, A, B, C, we may get A and B without C, A and C without B, B and C without A.

(5) Very few lines are strongly affected at the same time in the same spot, although a great many lines of the same substance may be affected, besides the twelve recorded as most widened on each day.

(6) Many of the lines seen in the spots are visible at low temperatures (some in the oxy-hydrogen flame), and none are brightened or intensified when we pass from the temperature of the electric arc to that of the electric spark.

(7) Certain lines of a substance have indicated rest, while other adjacent lines seen in the spectrum of the same substance in the same field of view have shown change of wave-length.

(8) A large number of the lines seen in spots are common to two or more substances with the dispersion employed.

(9) The lines of iron, cobalt, chromium, manganese, titanium, calcium, and nickel seen in the spectra of spots are usually coincident with lines in the spectra of other metals with the dispersion employed, whilst the lines of tungsten, copper, and zinc seen in spots are not coincident with lines in other spectra.

(10) The lines of iron, manganese, zinc, and titanium most frequently seen in spots are different from those most frequently seen in flames, whilst in cobalt, chromium, and calcium the lines seen in spots are the same as those seen in flames.

(11) Towards the end of the first series of investigations there appeared among the most widened lines a few which are not represented, so far as is known, among the lines seen in the spectra of terrestrial elements. This change took place when there was a marked increase in the solar activity.

(12) The most widened lines in sun spots change with the sunspot period.

(13) At and slightly after the minimum the lines are chiefly known lines of the various metals.

(14) At and slightly after the maximum the lines are chiefly of unknown origin.

(15) On the hypothesis under discussion the change indicates an increased temperature in the spots at the sun-spot maximum.

The general result is that in passing from minimum to maximum the lines most affected change from those of the ordinary chemical elements to lines whose significance are not known. The accompanying diagram represents graphically the disappearance of the lines of iron, nickel, and titanium and the simultaneous appearance of unknown lines in the spot spectra in passing from minimum to maximum. In the region of the spectrum for which the curves are drawn six lines were recorded in each observation, and therefore 600 in each series of 100 observations. In the curves the vertical ordinates represent not merely the number of individual lines recorded but the number of occurrences of lines of each substance. The dotted curve shows the variation in the frequency of the iron lines; at the minimum in 1879 practically all the 600 lines observed were iron lines; towards the end of 1881 they had dwindled down to 30; and during the three following years they fell to 10. The dot and dash curve shows a similar variation in the nickel lines, and the double line curve that of the titanium lines during the same periods. The continuous curve shows the gradual increase in the number of occurrences of unknown lines in passing from the minimum in 1879 to the maximum in 1884.

The chromosphere when quite quiescent merely gives us a spectrum of hydrogen together with a line in the yellow, which, from its proximity to D 1 and D 2 , is called D 3 . The chromosphere is disturbed in two ways,—first, by prominences, of which more hereafter, and second, by the formation gradually and peacefully of domes, which are of no great height but sometimes extend over large areas and last for weeks. These last-named phenomena have been termed “wellings up,” the idea being that they were produced by the gradual uprise of vapours from below; but it is clear that the same phenomena might be produced by the very slow descent of matter from above. The spectrum of these higher portions of the chromosphere, whether produced from below or above, is more complicated than the ordinary one. The following table (C) gives the principal lines which have been recorded up to 1887 :— [table]

The first new line in this table is called in spectroscopic language 1474, because when this work was begun the only maps available were those made by Professor Kirchhoff, and this particular line fell at 1474 on his scale. Since then these artificial scales have been discarded in favour of the natural one, which is given by the wavelengths of light of different colours. In this the reference number of the same line is 5315·9, which represents the wave-length in ten-millionths of a millimètre of that particular quality of light. After this we observe three lines of magnesium, only 3 out of 7; next a line of nickel, one only, however, out of 34; then two lines of sodium, although we might naturally expect to get all the 8 lines; then two lines of barium out of 26; and so on. Almost all the other lines have origins which are absolutely unknown: that is to say, we never get them in our terrestrial laboratories, and never, therefore, are able to match the bright lines in the chromosphere of the sun with any chemical substance. In 1871 the sun was more active, and this activity resulted in the addition of new lines, all, however, absolutely unknown to us, except one, which represents a line in the spectrum of titanium; but in that case we get one line out of 201 in exactly the same way as we get two only of iron out of 460. It is most important to note that practically none of the lines shown in table C are among those which are widened in spots.

The prominences are of two kinds—those which are relatively quiet and give almost exclusively the lines of hydrogen and those in which the motions are as a rule very violent. The spectrum of the latter class generally includes a large number of metallic lines; hence they are generally called metallic prominences. The first stage of metallic prominence is usually the appearance of three lines of the following wave-lengths—4943, 5031, 5315·9. As the prominence increases in magnitude and violence other lines are added, until at times the spectrum seems full of lines. The rate of uprush of these prominences sometimes reaches 250 miles per second, or nearly a million miles an hour,—figures which convey an idea of the enormous energies involved. The lines seen in these prominences, although many are present in the spectra of the metallic elements, appear with greatly changed intensities: the lines seen brightest in the prominences are frequently dim lines in the terrestrial spectrum. Again it may be remarked that these are not the lines which are most widened in spots. In the case of the spectrum of any one substance the number of lines seen usually in the prominences is very small.

The general conclusions which have been derived from a discussion of the prominence observations made by Profs. Tacchini and Riccò, in connexion with the sun-spot observations already mentioned, are as follows.

(1) The chromospheric and prominence spectrum of any one substance, except in the case of hydrogen, is unlike the ordinary spectrum of the substance. For instance, we get two lines of iron out of 460.

(2) There are inversions of lines in the same elements in the prominences, as there are inversions in the spots: in certain prominences we see certain lines of a substance without others; in certain other prominences we see the other lines without the first.

(3) Very few lines are strongly affected at once, as a rule, and a very small proportion altogether,—smaller than in the case of spots.

(4) The prominences are less subject to sudden changes than spots, so far as lines of the same element are concerned.

(5) There is a change in the lines affected according to the sun’s spot period.

(6) The lines of a substance seen in the prominences are those which in our laboratories become considerably brightened when we change the arc spectrum for the spark spectrum.

(7) None of the iron lines ordinarily visible in prominences are seen at the temperature of the oxy-hydrogen flame. Some of the oxy-hydrogen flame lines are seen in the spots, but none have ever been seen in the prominences.

(8) A relatively large number of the lines ordinarily seen are of unknown origin.

(9) Many of the lines seen are not ordinarily seen amongst the Fraunhofer lines. Some are bright lines.

(10) As in the spots the H and K lines of calcium in the ultraviolet are always bright in the spot spectrum, the other lines of calcium and the other substances being darkened and widened, so it would appear that the lines H and K of calcium are always bright in the prominences in which the other lines are generally unaffected.

(11) Many of the lines are common to two or more elements with the dispersion which has been employed.

The spectrum of the inner corona indicates that it is chiefly composed of hydrogen. All the hydrogen lines are seen in it, and up to a certain height the H and K lines of calcium, proving the presence either of calcium or of something that exists in calcium which we cannot get at in our temperature.

In the outer corona most of the hydrogen lines disappear; but one, the green line F, remains for a considerable height side by side with the 1474 line, indicating, as far as we can see where everything is so doubtful, that the constituents of the outer corona consist most probably of hydrogen in a cool form and the unknown stuff which gives the 1474 line. We also know that the outer corona contains particles which reflect the ordinary sunlight to us, because in 1871 Dr Janssen, and in 1878 Professor Barker and others, saw the dark Fraunhofer lines in the spectrum of the corona. We must imagine, therefore, that some part of that spectrum depends for its existence on solid particles which not only give a spectrum like that of the lime-light but have the faculty of reflecting to us the light of the underlying photosphere. It was also put beyond all question in the eclipse of 1882 in Egypt that this corona has another spectrum of its own. There are bright bands in the spectrum, showing that with these additions it is not a truly continuous spectrum like that of the lime-light, and that its origin is therefore in all probability very complex.

Association and Distribution of Phenomena.

Observations of prominences, spots, and other phenomena which require continuous investigation have been carefully made from day to day for several years, and one conclusion arrived at is that when and where the (disturbed) spots are at the maximum the faculae and metallic prominences are also at the maximum. When the maximum changes from north to south latitude in the spots it also changes from north to south in the metallic prominences and the faculae. These observations, therefore, establish not only an important connexion between spots, metallic prominences, and faculae but also the fact of the wonderful localization of these phenomena upon the sun. The spots are never seen higher in latitude than 40° north or south, and they are invariably seen in smaller quantity at the equator. Similarly, the faculae and metallic prominences do not go much beyond 40° north or south, and their minima are also at the equator. But this does not hold good for prominences of the quiet sort and the veiled spots,—that is, spots without umbrae or very highly developed penumbrae. They extend from one pole of the sun to the other; hence there must exist a great difference between metallic and quiet prominences and between disturbed and veiled spots.

Although the more important of these solar phenomena are limited to certain zones of the sun’s surface, and although they vary very violently, they have a cycle or regular succession of changes, during which the particular zone of the sun on which they appear alters. When there is the smallest number of spots on the sun—that is to say, when there is a sun-spot minimum—the spots that appear are seen in a high latitude, and the latitude decreases gradually until we arrive at the next minimum. Thus there are two perfectly distinct spotted areas, one corresponding to the end of the old period, the other to the beginning of the new period. At the maximum period of sun spots the latitude of the spot zone is about 15°. Activity in the solar atmosphere, therefore, appears to begin in a high latitude—say about 30° or 35°—and very soon reaches the maximum in about latitude 15°; then it gradually dies away until spots, metallic prominences, and faculae—all of reduced intensity—cling pretty near to the solar equator, and at the same time we get a new wave of activity, beginning again in a high latitude. This association of what may be called localized phenomena is quite in harmony with a similar association of phenomena which are more or less generally distributed over the whole surface of the sun.

Pores, which are in reality nothing but small sun spots, may occur in any part of the sun, and are always accompanied by a slight waviness in the chromosphere. Veiled spots—spots which never attain full development—are also universally distributed over the sun’s surface and are accompanied by small prominences (see below).

The main periodicity on the sun is that of about eleven years which elapses...

The Nectariniidae form the subject of a sumptuous Monograph by Capt. Shelley (4to, London, 1876-1880), in the coloured plates of which full justice is done to the varied beauties which these gloriously arrayed little beings display, while, almost every available source of information having been consulted and the results embodied, the text leaves little to be desired, and of course supersedes all that had before been published about them. This author divides the Family into three subfamilies :— Neodrepaninae, consisting of a single genus and species peculiar to Madagascar; Nectariniinae, containing 9 genera, one of which, Cinnyris, has more than half the number of species in the whole group; and Arachnotherinae (sometimes known as “Spider-hunters ”), with 2 genera including 11 species— all large in size and plain in hue. To these he also adds the genus Promerops , composed of 2 species of SouthAfrican birds, of very different appearance, and the affinity of which to the rest can as yet hardly be taken as proved. According to Mr Layard, the habits of the Cape Promerops, its mode of nidification, and the character of its eggs are very unlike those of the ordinary Nectariniidae. In the

British Museum Catalogue of Birds (vol. ix. pp. 1-126, and 291) Dr Gadow has more recently treated of this Family, reducing the number of both genera and species, though adding a new genus discovered since the publication of Capt. Shelley’s work. (a. n.)

few years later D’Aubenton figured it in his well-known series (Pl. Enl., 782), and then in 1781 came Buffon (H . N., Oiseaux, viii. pp. 169, 170, pl. xiv.), who, calling it “Le Caurâle ou petit Paon des roses,” announced it as hitherto undescribed, and placed it among the Rails. In the same year appeared the above-cited paper by Pallas, who, notwithstanding his remote abode, was better informed as to its history than his great contemporary, whose ignorance, real or affected, of his fellow-countryman’s priority in the field is inexplicable; and it must have been by inadvertence that, writing “roses” for “roseaux,” Buffon turned the colonial name from one that had a good meaning into nonsense. In 1783 Boddaert, equally ignorant of what Pallas had done, called it Scolopax solans, and in referring it to that genus he was followed by Latham (Synopsis, iii. p. 156), by whom it was introduced to English readers as the “Caurale Snipe.” Thus within a dozen years this bird was referred to three perfectly distinct genera, and in those days genera meant much more than they do now. Not until 1811 was it recognized as forming a genus of its own. This was done by Illiger, whose appellation Buryρyga has been generally accepted.

The Sun-Bittern is about as big as a small Curlew, but with much shorter legs and a rather slender, slightly decurved bill, blunt at the tip. The wings are moderate, broad, and rounded, the tail rather long and broad. The head is black with a white stripe over and another under each eye, the chin and throat being also white. The rest of the plumage is not to be described in a limited space otherwise than generally, being variegated with black, brown, chestnut, bay, buff, grey, and white—so mottled, speckled, and belted either in wave-like or zigzag forms as somewhat to resemble certain moths. The bay colour forms two conspicuous patches on each wing, and also an antepenultimate bar on the tail, behind which is a subterminal band of black. The irides are red; the bill is greenish olive; aud the legs are pale yellow. As in the case of most South-American birds, very little is recorded of its habits in freedom, except that it frequents the muddy and wooded banks of rivers, feeding on small fishes and insects. In captivity it soon becomes tame, and has several times made its nest and reared its young (which, when hatched, are clothed with mottled down; Proc. Zool. Society, 1866, p. 76, ρl. ix. fig. 1) in the Zoological Gardens (London), where examples are generally to be seen and their plaintive piping heard. It ordinarily walks with slow and precise steps, keeping its body in a horizontal position, but at times, when excited, it will go through a series of fantastic performances, spreading its broad wings and tail so as to display their beautiful markings. This species inhabits Guiana and the interior of Brazil; but in Colombia and Central America occurs a larger and somewhat differently coloured form which is known as E. major.

For a long while it seemed as if Eurypyga had no near ally, but, on the colonization of New Caledonia by the French, an extremely curious bird was found inhabiting most parts of that island, to which it is peculiar. This the natives called the Kagu, and it is the Rhinochetus jubatus of ornithology. Its original describers, MM. Jules Verreaux and Des Murs, regarded it first as a Heron and then as a Crane (Rev. et Mag. de Zoologie, 1860, pp. 439-441, pl. 21; 1862, pp. 142-144); but, on Mr George Bennett sending two live examples to the Zoological Gardens, Mr Bartlett quickly detected in them an affinity to Eurypyga (Proc. Zool. Society, 1862, pp. 218, 219, pl. xxx.), and in due time anatomical investigation showed him to be right. The Kagu, however, would not strike the ordinary observer as having much outward resemblance to the Sun-Bittern, of which it has neither the figure nor posture. It is rather a long-legged bird, about as large as an ordinary Fowl, walking quickly and then standing almost motionless, with bright red bill and legs, large eyes, a full pendent crest, and is generally of a light slate-colour, paler beneath, and obscurely barred on its longer wing-coverts and tail with a darker shade. It is only when it spreads its wings that these are seen to be marked and spotted with white, rust-colour, and black, somewhat after the pattern of those of the Sun-Bittern. Like that bird too, the Kagu will, in moments of excitement, give up its ordinary placid behaviour and execute a variety of violent gesticulations, some of them even of a more extraordinary kind, for it will dance round, holding the tip of its tail or of one of its wings in a way that no other bird is known to do. Its habits in its own country were described at some length in 1863 by M. Jouan (Mém. Soc. Sc. Nat. Cherbourg, ix. pp. 97 and 235), and in 1870 by M. Marie (Actes Soc. Linn. Bordeaux, xxvii. pp. 323-326), the last of whom predicts the speedy extinction of this interesting form, a fate foreboded also by the statement of Messrs Layard (Ibis, 1882, pp. 534, 535) that it has nearly disappeared from the neighbourhood of the more settled and inhabited parts.

The internal and external structure of both these remarkable forms has been treated in much detail by Prof. Parker in the Zoological Proceedings (1864, pp. 70-72) and Transactions (vi. pp. 501-521, pls. 91, 92; x. pp. 307-310, pl. 54, figs. 7-9), as also by Dr Murie in the latter work (vii. pp. 465-492, pls. 56, 57), and the result of their researches shows that they, though separable as distinct l·amilies, Eurypygidae and Phinochetidae, belong to Prof. Huxley’s Geranomorphae, of which they must be deemed the relics of very ancient and generalized types. Their inter-relations to the Rallidae (Rail, vol. xx. p. 222), Psophiτdse (Trumpeter, q.v. ) , and other groups there is not space here to consider, any more than there is to speculate on the bearings of their geographical position. It is only to be remarked that the eggs of both Eurypyga and Rhinochetus have a very strong Ralline appearance— stronger even than the figures published (Proc. Zool. Society, 1868, pl. xii.) would indicate. (a. n.)

Sun-fishes are truly pelagic, propagating their species in the open sea, and only occasionally approach the coast. During the stormy season they live probably at some depth, but in calm bright weather they rise and rest or play on the surface with their dorsal fin high above the water. This habit has given rise to the popular name “sun-fish,” a term also sometimes applied to the basking-shark (vol. xxi. p. 777), which in like manner enjoys the warmth of a sunny day. In some years the rough sun-fish is by no means scarce on the south coast of England and on the Irish coasts, where it appears principally in the summer months. The usual size is from 3 to 4 feet in length, but this species attains to 7 feet and more. One of the largest specimens (see the accompanying figure) was caught near Portland (Dorsetshire) in 1846, and is now in the British Museum; its length is 7 feet 6 inches. The sun-fish has no economic value, and is rarely, if ever, eaten.

Whilst the rough sun-fish has a granulated, rough, shagreen-like skin, the second species (O. truncatus) has the surface of the body smooth and polished, with its small dermal scutes arranged in a tesselated fashion. It is oblong in shape, the body being much longer than it is deep. The sides are finely ornamented with transverse silvery, black-edged stripes running downwards to the lower part of the abdomen. It has not been found to exceed 2 feet in length, but is very scarce, only a few specimens having been captured on the coasts of Europe, at the Cape of Good Hope, and off Mauritius.