At the eclipse of 1851 a large number of observers attended; and in the year 1860 there was a government expedition to Spain, and 40 observers went there from this country alone, while Norway, France, and the United States all sent expeditions; and from this time forward, no opportunity, however remote, has been neglected.

An eclipse has always been regarded with popular favour as affording ocular evidence of the accuracy of the calculation of the time of conjunction of the sun and moon, but in the period under review the interest has been transferred from the mathematical to the physical side of the question, owing to the desire to understand something of the nature of the centre of life of our system.

Hofrath Schwabe, of Dessau, was the originator of this line of research, for which he was awarded the gold medal of the Royal Astronomical Society in the year 1857.

Imbued with the idea of discovering an intra-Mercurial planet, this indefatigable observer, beginning in 1826, and continuing for 43 years, rarely missed an opportunity of examining the sun on every day when he was visible.

No success attended this pursuit, but as has frequently happened in the history of science, his critical inspection of the sun's spots led to a discovery of superior value, viz., that of their periodicity—as he himself quaintly observes, "like Saul, in seeking his father's asses, I found a kingdom."

The work thus inaugurated has been continued to the present time, and auto-photographic records of the sun's appearance are made at several places on each day. The collation of these, with independent records of magnetic variation which are continuously being tabulated, may, at some future time, lead to valuable results.

By far the most important discovery in solar physics is that achieved by Kirchoff in 1859, which, by showing the

meaning of the absorption bands (known as Fraunhofer lines) in the solar spectrum, opened the door to an infinity of research upon the nature of the elements of which the photosphere of the sun is composed; and since that day spectrum analysis has been the determining factor in the results attained by eclipse observations.

The use of photography, by which observations have not only been multiplied one hundred-fold, but rendered unbiassed by personal equation, has also been of the utmost importance; and a third method, which was first practised during the eclipse of 1898, in India, is that by studious concerted action of amateur observers, long prior to the actual observations on the spot, of diagrams made to resemble various eclipse phases, a wonderful improvement has been found in the fidelity of sketches, made by hand, of the form and extent of the coronal rays when compared with similar drawings made in the absence of such systematic training.

The phenomena observed about the time of, and during totality, occur in the following order :

Firstly, the formation of Baily's Beads, seen only for a few seconds just as the moon is completely covering with her disc the body of the sun at the time of second contact (which is the commencement of totality), and, again, as totality is broken at the time of third contact. These "beads," which move rapidly along the edge of the two discs, are probably due to irradiation of the sun's intense light, possibly some diffraction effects being also mixed up with it. They are named after Mr. F. Baily, who first investigated them at the annular eclipse at Jedburgh in 1836.

Secondly, just at the moment of totality the chromosphere flashes out, as a narrow ring of brilliant rose coloured light round a portion of the edges of the sun and

moon. The angular extent of this arc of light depends upon the relative diameters (apparent) of the sun and moon, for, as the depth of illuminated stratum does not exceed a few seconds of arc, it is manifest that if the eclipse were just central for a second, this coloured layer might be seen all round the moon's edge, and, conversely, if the totality is of long duration, it might scarcely appear at all. There are always some parts of the chromosphere in a state of great commotion, visible as red prominences, which vary in number and shape on every such occasion— these prominences assume the most grotesque forms, and frequently flame out to a height of over 100,000 miles above the chromosphere.

The third feature of the display is the appearance of the corona coincidentally with totality-this is a faint pearly effulgence, which varies in shape and extent at every eclipse, and is by far the most conspicuous of eclipse phenomena.

A combination is thus presented to the bewildered spectator of unwonted weirdness and grandeur which renders the vision of a total eclipse of the sun the most exciting spectacle afforded by the magnificence of nature, one never to fade from the memory of the favoured observer. It is in the midst of such a scene that science has calmly to perform her duties, and to beware lest one precious moment of time be wasted.

With this general review, we may now pass to a consideration of the order of discoveries by which our present knowledge of the physical condition of the sun has been attained.

It was at the eclipse of 1851 that the red prominences, which were very active and appeared at a great height above the sun's circumference, were believed to be Solar and not Lunar phenomena, and this opinion was proved

conclusively in the year 1860, when Mr. Warren de la Rue, at Riva Bellosa, and Mr. Aguilar, at Desierto de las Palmas, by means of timing the movement of the moon on plates taken at stations 250 miles apart, settled the question finally.

The eclipse of 6th March, 1867, was not a total one, but it was signalized by the observation of a prominence by Ensign Kiha a quarter-hour before the annular phase was established-than which no better proof is possible of the brilliancy and intensity of these extraordinary objects.

In 1868, on 18th August, an eclipse was total for an unprecedentedly long period (6m. 50s.) in India, and an enormous amount of work was done-the gaseous nature of the prominences was established by several observers on the first application of the spectroscope-the work being assisted by the remarkable nature of the prominences then seen. Hydrogen gas, as expected, was ascertained to be one of their constituents.

On 20th Oct. of same year, 1868, Mr., now Sir, Norman Lockyer announced the possibility of seeing the bright lines in the solar prominences without an eclipse, and on the following day M. Janssen announced the same fact to the Paris Academy, with the further information that he had made the discovery the day after the eclipse, viz., 19th August, 1868. Truly a remarkable coincidence.

In the year 1870, 22nd December, a total eclipse in Spain, Sicily, and Africa was rendered noteworthy by the fact that the same two astronomers had curious adventures. M. Janssen made his escape from the siege of Paris in a balloon, with a special instrument for viewing the totality in Algeria, but, through bad weather, was unable to use it, for, as Miss A. Clerke says, "He reached Oran only to find himself shut behind a cloud curtain more impervious than the Prussian lines; " while Mr.

Lockyer, on the way to Sicily, was shipwrecked in the Psyche, and only succeeded in obtaining a fleeting glimpse of the wonders of the corona.

Persistent spectroscopic attacks on the prominences have revealed the fact that they consist of glowing hydrogen and some other gases, and have their source in, and rest upon, the chromospheric layer of similar gases; this consists of a thin spherical shell, covering the sun's surface everywhere to a depth of from 2,000 to 6,000 miles.

At this eclipse a further most important discovery was made, that of the "reversing layer."

The method of discovery is as follows:-Just before the second contact the dark body of the moon rapidly closes up the narrow crescent of light remaining on the sun's disc, and it finally goes out; at the very moment this happens, for a space of time not exceeding a couple of seconds, the vanishing absorption spectrum of the sun is instantly changed, line for line of the ordinary solar spectrum, into a bright line spectrum, and this wonderful appearance (not visible to the naked eye, of course) is one of the most entrancing sights among all the beauties of totality. This sight only lasts while the moon passes over about 800 miles of solar surface, which occupies only two seconds, the height of this "layer" being thereby accurately defined. This discovery was a testimony to the prescience of Kirchoff, for, as Miss Clerke says, "A 'reversing layer' or stratum of mixed vapours glowing, but at a lower temperature than that of the actual solar surface, was an integral part of Kirchoff's theory of the production of the Fraunhofer lines."

Calcium vapor was discovered in 1882, and, later, manganese, iron, and carbon (probably) have been added to the list.

Lockyer, during the year 1900, investigated the heights