hours in a state of unusual brilliance and excitement, and showed in the spectroscope more than 120 bright lines whose position was determined and catalogued-all that I had ever seen before and some 15 or 20 besides." Before passing from the prominences it may be well to indicate the laws of their numerical distribution, as determined by Secchi and others. This is shown in fig. 3. On the left side the results of Carrington's observation of 1,414 spots between 1853 and 1861 are indicated, and on the right the result of Secchi's

Sept. 7, 1871.

the number of spots or prominences being of course shown by the length of the radial lines. The dotted line on the right-hand side represents in the same manner the distribution of the larger prominences, viz., those exceeding 1' or 27,000 m. in height.-During a total eclipse there appears around the black body of the moon a halo or glory of light, bright, close to the place of the concealed sun, but gradually fading away outward, until its light is lost in the general tint of the sky. In this glory of light, which is called the solar corona, radiations are also sometimes seen, and under favorable atmospheric conditions complicated series of streaks can be seen extending to a considerable distance outward from the prominence region. Various theories were advanced in former times to explain the corona. According to one theory, it is a phenomenon caused by the solar light falling on our own atmosphere; another theory ascribed it to a lunar atmosphere. In the opinion of Leverrier and Foucault (among others), the corona is an example of the interference of light (see LIGHT), the phenomenon being analogous to the colored fringes seen on a screen in a darkened room when a solar beam is admitted

182

through a chink. To this theory Airy raised the objection that if, in order to make the analogy perfect, the eye is placed in the position of the screen, no colored fringes are seen. It is shown that the corona is partly polarized, and hence partly consists of reflected light. It has been further proved that the plane of polarization passes through the sun and the observer. This was regarded by Airy as pointing to the existence of an atmospherie medium capable of reflecting light, and extending from the earth to the moon. But in more recent times astronomers began to perceive that no other theory can be admitted than that which regards the corona as a true solar appendage. (Of course, it must be admitted that a portion of the light around the eclipsed sun comes from our own atmosphere, which must necessarily be illuminated by the true corona

during eclipse, precisely as it is illuminated by the sun when there is no eclipse; but it will readily be understood that this portion of reflected light is very small in amount.) During the solar eclipse of August, 1869, Profs. Young and Harkness discovered that certainly one bright line exists in the spectrum of the corona, and two other lines were suspected. European astronomers expressed doubt as to the accuracy of this observation; but it was confirmed du- | ring the Mediterranean eclipse of December, 1870, when Young thus summed up his own and other observations: "There is surrounding the sun, beyond any further reasonable doubt, a mass of self-luminous gaseous matter, whose spectrum is characterized by the green line 1,474 Kirchhoff. The precise extent of this it is hardly possible to consider as determined, but it must be many times the thickness of the red hydrogen portion of the sierra, perhaps on an average 8' or 10', with occasional horns of twice that height. It is not at all unlikely that it may even turn out to have no upper limit, but to extend from the sun indefinitely into space." During the same eclipse, Brothers of Manchester and Willard of Philadelphia (the latter acting under the directions of Prof. Winlock of the Harvard observatory) photographed the corona successfully from two distant stations, Willard being near Jerez in Spain, Brothers near Syracuse in Sicily. The views thus obtained agreed so closely (save in circumstances depending on photographic conditions) as to leave no doubt that the corona is a solar phenomenon. Doubts were still expressed, and it was not until the solar eclipse of December, 1871, that these were finally removed. On that occasion the spectroscopic and photographic results were alike decisive. Janssen with the spectroscope not only recognized the bright lines before seen and others less bright, but also a faint solar spectrum, which, since our atmosphere during total eclipse is certainly not illuminated by sunlight, must have been reflected by matter in the solar corona, such as vaporous clouds, meteor flights, or the like. Mr. Davis, a photographer sent out at Lord Lindsay's expense, obtained five excellent photographs of the corona, all agreeing perfectly inter se, excepting in extent. This proved certainly that the features of the corona do not change as they would if the phenomenon depended on the passage of light rays athwart lunar inequalities, to fall upon scattered matter at a less distance than the moon. Again Col. Tennant obtained six photographs, similarly accordant inter se, and also agreeing perfectly with Mr. Davis's at Dodabetta, a station far removed from Davis's, Baicull. Since, also, Dodabetta is near the highest peak of the Neilgherries, about 9,000 ft. above the sea level, while Baicull is close to the seashore, it will be manifest that if the features of the corona depended on the illumination of our own atmosphere, the pictures of Tennant's series would have differed altogether from those

of Davis's series. Thus, independently of the spectroscopic evidence, the photographs proved that the corona is a solar appendage, at least as far as those features shown in the two series extend. But they extend from the sun in places to a distance exceeding his own diameter, and amounting in fact to more than a million miles. There is reason to believe that the true solar corona extends much further, and that in reality the zodiacal light (see ZODIACAL LIGHT) forms the outer part of the solar corona; so that if the light of the sun could be for a time obliterated without rendering his appendages invisible, we should see the corona merging gradually into the faint glow of the zodiacal light. Mr. Arthur W. Wright of Yale college has succeeded in showing that this light is not emitted from incandescent gas, but reflected from particles or small bodies, and hence derived from the sun.-Another important discovery made during total solar eclipses relates to a solar atmosphere underlying even the sierra. Secchi had observed in 1869 that close to the sun's limb the solar spectrum becomes continuous; this he considered to be due to the existence of a relatively very shallow atmosphere, consisting of the vapors which cause the dark lines of the solar spectrum. For if the brightness of the lines of these vapors corresponds very closely to the brightness of the ordinary solar spectrum for the parts near to the sun's edge, the dark lines of the latter spectrum would be cancelled, and so a continuous spectrum would be produced. For another reason, the present writer had adopted the theory that the atmosphere producing the absorption lines of the solar spectrum must be shallow, compared at least with the dimensions of the sun's globe; for he showed that a shallow and not a deep atmosphere is to be inferred from the darkening of the solar disk near its edge. The opinion thus advanced on theoretical grounds was shown to be correct by the observations of Prof. Young during the total eclipse of December, 1870; for, "directing his analyzing spectroscope to the part of the sun's limb which was to disappear last, he found that at the instant when totality commenced the solar spectrum was suddenly replaced by a spectrum consisting of a thousand soft bright lines." In other words, the vapors which by their absorptive action produce the dark lines of the ordinary solar spectrum were for the moment shining with their own light, and thus produced a spectrum of bright lines. This spectrum continued visible for a few seconds only, showing that the complex atmosphere producing it cannot be more than two or three hundred miles in depth. The observation was successfully renewed during the eclipse of December, 1871, and again during the annular eclipse of June, 1872.-How to account for the supply of the prodigious amount of heat constantly radiated from the solar surface has offered a boundless field of hypothesis. One conjecture

has been that the sun is now giving off the heat imparted to it at its creation, and that it is gradually cooling down; another ascribed it to combustion, and a third to currents of electricity. Newton and Buffon conjectured that comets might be the aliment of the sun, and of late years a somewhat similar theory (first broached by Mr. Waterston in 1853) has been in vogue, viz., that a stream of meteoric matter constantly pouring into the sun from the regions of space supplies its heat, by the conversion into it of the arrested motion. As the sun may indeed derive a small amount of heat from this cause, it deserves more attention than previous conjectures. But conjecture and hypothesis may be said to have given place to views which claim a higher title, as it is now becoming generally recognized, in accordance with modern physical theories of heat, that in the gravitation of the sun's mass toward its centre, and in its consequent condensation, sufficient heat must be evolved to supply the present radiation, enormous as this undoubtedly is. It appears to be susceptible of full demonstration that a contraction of the sun's volume | of a given definite amount, which is yet so slight as to be invisible to the most powerful telescope, is competent to furnish a heat supply equal to all that can have been emitted during historical periods. According to this theory then (which is due largely to the development by Helmholtz of Mayer's great generalization), the sun's mass remains unaltered, and its temperature nearly constant, while its size is slowly diminishing as it contracts; so slowly, however, that the supply may be reckoned on through periods almost infinite as measured by the known past of our race, and which are in any case to be counted by millions of years. It would appear from early measurements of Secchi that the different portions of the solar disk do not radiate heat in uniform degrees, and his tables show that the equatorial regions are slightly hotter than the polar. It has been explained that the rapid decrease of brightness toward the edge of the sun obliges us to admit the existence of a shallow atmosphere around it. Prof. Langley has recently published tables from more extended measurements, showing the rate of absorption both of heat and light, the latter being greater than the former. As he does not now find the difference between the equatorial and polar heat observed by Secchi in 1852, the latter concludes from a comparison of his own observations with Langley's, that great changes occur in the distribution of the heat on the sun's surface. Prof. Langley has further shown that this atmosphere absorbs one half of the sun's total radiation, and he considers that its function in the solar emission is of great importance to us. A slight alteration in the thickness of this obscuring envelope would induce changes on the earth greater than those known to have occurred in its climate in past geologic epochs, which may themselves not impossibly

|

have been due to this hitherto unrecognized cause. M. Fizeau has found that the chemical rays are similarly reduced in amount toward the edge of the solar disk, a fact which is also abundantly shown by the darkening near the edge of photographic sun pictures, like those by Rutherfurd and De la Rue.-To sum up briefly the received hypotheses of the physical constitution of the sun: Of its internal structure we know nothing, but we can infer from the low density of the solar globe as a whole that no considerable portion is solid or liquid. The regions we examine appear to consist of cloud layers at several levels floating in a complex atmosphere, in which probably most of the elements are known to us, and certainly many of them exist in the form of vapor. Outside this complex atmosphere extend envelopes of simpler constitution, though into them occasionally arise the vapors which ordinarily lie lower down. The sierra, for instance, consists in the main of glowing hydrogen gas, and that gas, whatever it may be, which produces the line near the orange-yellow sodium lines. The prominence region may be regarded as simply the extension of the sierra. The inner corona is still simpler than the sierra so far as its gaseous constitution is concerned; but here meteoric and cometic matter appears, extending to the outer corona and to great distances beyond even the visible limits of the zodiacal. Returning to the photosphere, we find it subject to continual fluctuations, both from local causes of agitation and from the subjacent vapor acting by its elasticity to burst through it; the faculæ, which are found to be above the general level of the photosphere, are taken to be heapings up of the luminous matter like the crested surges of the sea. All the strata are subject to great movements, which sometimes have the character of uniform progression analogous to our trade winds, and sometimes are violent and resemble in their effects our tornadoes and whirlwinds. Eruptive action appears to operate from time to time with exceeding violence, but whether the enormous velocities of outrush are due to true explosive action (which would compel us to believe that the sun is enclosed by a liquid shell, so as to resemble a gigantic bubble), or to the uprising of lighter vapors from enormous depths, as heated currents rise in our own atmosphere, is not as yet known. (See supplement.)

SUN BIRD, the name commonly given to the promeropida, a family of tenuirostral birds, with a long, slender, and usually curved bill, the nostrils placed at the base and covered with a scale, wings of moderate size, and short tarsi covered with broad scales. They inhabit the tropical regions of both hemispheres; the subfamily promeropinæ, including by far the most species, is confined to the old world, and the carebine to the new. The true sun birds belong to the former, and have a long, slender, curled, and sharp bill, sometimes finely serrated on the margins; the tail is long, the central

feathers often exceeding the rest. They are found in the islands of the Pacific and Indian oceans, and on the continents of Africa and Asia; they are the humming birds of the old

Fiery-tailed Sun Bird (Nectarinia ignicauda).

world, having similar habits and the same brilliant colors, but are larger. The genus nectarinia (Illig.) contains more than 100 species, mostly African. The nest, of an elegant form, is usually suspended from the end of a twig, with an opening at the side; the eggs are two to four. The carebina or guitguits have a shorter, broader, and nearly straight bill, and long pointed wings; they are found in tropical South America and the West Indies; the plumage is very beautiful. The nest is protected by a long funnel or by two compartments against insects, birds, serpents, and lizards.

SUNBURY, a borough and the capital of Northumberland co., Pennsylvania, on the E. bank of the Susquehanna river, 42 m. N. of Harrisburg, and 114 m. N. W. of Philadelphia; pop. in 1870, 3,131. It has a daily and three weekly newspapers, and several manufactories and machine shops. It is connected by rail with Philadelphia and the Shamokin mining region, and about 200,000 tons of coal are shipped annually.

SUNBURY, & S. central county of New Brunswick, Canada, intersected by the St. John river; area, 1,203 sq. m.; pop. in 1871, 6,824, of whom 2,839 were of English, 2,655 of Irish, and 552 of Scotch origin or descent. The surface is nearly level; the soil is fertile and heavily wooded. The European and North American railway and Fredericton branch traverse the county. Capital, Oromocto.

SUNDA ISLANDS, a former designation of those islands of the Indian archipelago which surround the Java sea. They were divided into the greater and the lesser Sunda islands, the former including Sumatra, Borneo, Celebes, and Java, and the latter the chain of islands which extends from the E. extremity of Java to Papua, exclusive of the Moluccas.

SUNDA STRAIT, an arm of the sea between 'the islands of Sumatra and Java, which leads from the Indian ocean to the Java sea. The length of the channel upon the Sumatra side,

from Flat point, in lat. 5° 59' S., to Hog point, is about 85 m.; and upon the opposite coast, from Java head, lat. 7° 5' S., to Bantam point, about 100 m. The breadth of the strait where it joins the Indian ocean is about 70 m., and at the end next the Java sea about 20 m.

SUNDAY (Sax. Sunnan dag), the first day of the week, identical with the Roman dies Solis (day of the sun). The keeping of this as a sacred day, in memory of Christ's resurrection and of the descent of the Holy Ghost, dates from the beginning of Christianity. It is probable that the first Jewish Christians kept this day holy, while conforming also to their legal sabbath. It was called the Lord's day in all the churches; but it was also popularly designated as Sunday as soon as the gentile element began to prevail. According to De' Rossi, the first monumental inscription calling it the Lord's day is of the year 403. Its first official recognition is in an edict of Constantine in 321, ordering that all work should cease in the cities "on the venerable Sunday," but permitting necessary husbandry to be attended to. The Theodosian code prescribed that "on the Sunday, rightfully designated by our ancestors as the Lord's day, all lawsuits and public business shall cease." (See LORD'S DAY.)

SUNDAY SCHOOLS. The earliest recorded Sunday schools were the schools of catechumens, organized, according to Tertullian, in A. D. 180, though less formal instruction of Christian children and novitiates prevailed earlier. The schools of the catechumens flourished till the 6th century. In 1527 Luther established Sunday schools in Wittenberg for the instruction of children who could not attend the day schools. In 1560 Knox inaugurated them in Scotland. In 1580 Archbishop Borromeo of Milan established a system of Sunday schools throughout his diocese, and about the same time there were similar schools in France and the Netherlands. In the 17th century the clergy statedly catechised the children in some parishes of England; and Joseph Alleine, author of the "Alarm," opened a Sunday school in 1668. There was a Sunday school in Roxbury, Mass., in 1674, and one in Plymouth, Mass., in 1680. About 1740 Ludwig Hacker established a school in Ephratah, Lancaster co., Pa., which continued until the building was taken for a hospital during the revolution. Modern Sunday schools, however, were originated by Robert Raikes, who in 1781 gathered poor children from the streets in Gloucester, England, and employed female teachers at a shilling a day for their instruction. The children were taught from 10 A. M. to 12; then, after an hour's recess, read a lesson and went to church. After church they repeated the catechism till after 5, and were then charged to go home at once and quietly. Raikes published an account of his work in the "Gloucester Journal" in 1783, which was republished in the "Gentleman's Magazine," and schools upon his plan were soon estab