to which different gases ascend in the chromosphere, hydrogen, calcium and helium being the highest. The theory of the corona cannot be said to be in an advanced state. It has presented many more difficulties to the observer than the chromosphere and prominences. It is very faint compared with the sun's light, and, although upon one or two memorable occasions it has been seen before and after totality, it has not been so amenable to investigation either by the camera or the spectroscope. It evidently varies in intensity greatly from time to time, for it is chiefly the light which it yields that illuminates the heavens at totality, and the reports of various eclipses show great differences in its brilliancy. It must have been very bright in 1851, when Busch, of Konigsberg, caught it upon a Daguerreotype plate. The next successful attempt was by Mr. Brothers, at Syracuse, 22nd December, 1870. In 1868, in India, the spectroscope was first applied to the corona, which was proved to be entirely different to the chromosphere in character. Again, in 1869, Prof. Harkness discovered in the continuous spectrum a single green ray, which, till now, has been a subject for endless controversy. This line was so nearly identical with one of the numerous iron lines that it was then considered that this heavy metal, in a gaseous state, was evident in the corona at a distance of at least a million of miles from the sun's surface. This view, however, has subsequently proved to be erroneous. In 1871 the sodium line was perceived as a dark line, and, at the same eclipse, Lockyer at Baikul, and Respighi at Poodacottah, perceived hydrogen in this substance 200,000 miles above the sun's surface, and established the fact that the corona "is of a highly complex construction, being made up in part of glowing vapours, in part of matter capable of reflecting sunlight." On 29th July, 1878, Professor Langley, at a height of 14,500 feet, on Pike's Peak, saw the corona four minutes after totality extending to a distance of ten millions of miles from the sun, i.e., more than ten times the sun's diameter in extent. This is a marvellous observation, which, though amply credited, has not since been repeated. In 1885, Dr. Huggins made experiments with the view of photographing the corona without total eclipse; although carried out in the clear air of the Riffelberg, success was not then nor has it since been attained. In 1887, the most extensive preparations ever made to view a total eclipse were attended by the most wide-spread disappointment; but at one place, Petrowsk, Professor Kononovitsch, of Odessa, succeeded in photographing the green line, provisionally known as 1474 K, or coronium (for want of a better name). Professor Ramsay, in 1895, discovered a terrestrial origin for Helium in the Norwegian Mineral "cleveite,” and so settled the character of many other coronal lines which till then had not been identified. Two total eclipses were observed in 1889-the first on 1st January from California, and the second on 22nd December from the West Indies. A well equipped party at Cape Ledo, in South Africa, from whose co-operation with those stationed in the Western hemisphere double photographs, intended to shew whether the shape of the corona underwent change in a space of two or three hours, was disappointed through bad weather. This eclipse entailed a serious loss to astronomy by the death of the Rev. S. J. Perry, of Stonyhurst College, who was well known to students of astronomy in this locality. Father Perry frequently attended the meetings of the Liverpool Astronomical Society, and was President for a year. (His devotion to duty was extreme, and was exemplified by the long and arduous expedition of which he took command to observe the transit of Venus at Kerguelen Island, in 1874.) On the occasion of this eclipse he occupied a station on the Isles du Salut, near Cayenne, where there was great mortality among the convicts. Although he became dangerously ill with the epidemic, his characteristic energy enabled him to use the last of his strength to carry through successfully the important observations, after which he was conveyed on board the Comus, but did not live to reach Demerara. The year 1896 was memorable for a new departure, in the despatch of an expedition by the British Astronomical Association (a society numbering over 1000), of 80 of its members to Vadsö, near the North Cape. Clouds unfortunately utterly obscured the sun during the whole of totality, and frustrated the principal object of the expedition. Their lack of fortune did not, however, prevent the despatch of another expedition, consisting of two parties, by the same society, upon a smaller scale (on account of the distance) to India for the eclipse of 22nd January, 1898. These were in every way successful (ride Indian Eclipse, 1898, E. Walter Maunder). On this occasion several important results were obtained, the most interesting perhaps being that Mrs. Maunder, on a small plate, obtained the greatest extension of the corona that has yet been photographed. One ray extending itself to a distance exceeding three-and-a-half times the sun's diameter. The third expedition promoted by this enterprising society was divided into no fewer than five distinct parties for the purpose of observing the total eclipse of 28th May, 1900. Stations were occupied by them in the United States, at sea, in Spain, Portugal, and Algeria. The Total Solar Eclipse, 1900, by E. Walter Maunder. Vide There is a part of the subject which is of extreme interest, and which is actively discussed after every eclipse, but which is by no means ripe for judgment, i.e., the connection which mutually subsists between the chromosphere, the prominences, and the corona; and also their liability to be affected by physical changes on the sun. There seems to be no doubt about the connection between sun-spots and prominences, but what the connection is between spots and the corona is not so manifest, though the character of the corona varies in type at maximum and minimum spot periods. The chromosphere and prominences apparently are subject to the vast attraction of solar gravitation, and the latter attain their enormous height by reason of the violence of their projection, and in spite of the attraction, but the corona is as undoubtedly not controlled by the sun's attraction, but chiefly caused by glare of solar light upon gases and matter that have been brought into his influence in ways about which at present it is not possible to come to any definite conclusion. In so cursory an attempt to exhibit the state of our knowledge of solar surroundings as revealed by eclipses, many points, for want of time, have been omitted, which might have rendered the subject clearer, especially details of spectroscopic researches upon terrestrial elements and upon gases at varying temperatures and densities, under which, to some extent (cum longo intervallo), solar conditions have been approximated to. It is through the continued application of spectroscopy to solar research at every eclipse that future progress appears most feasible. May we hope that, in a not far dis H tant future, the sciences of optics and chemistry may solve the difficult problem of showing how such research can be carried out without waiting for these rare and exciting opportunities. NOTE. References too numerous to point out in detail have been made to the following : : Grant's History of Physical Astronomy. History of Astronomy during the 19th Century, Miss A. M. Eclipses, Past and Future, Rev. S. J. Johnson, M.A. The Monthly Notices of the Royal Astronomical Society. |