as they appear moving in the sky, that meaning is correct and natural. If, moreover, our science is correct as to the progressive condensation of the sun, the luminous atmosphere would be cleared gradually during the sun's process of integration as a revolving light." The development of the earth is an analogue of the development of suns and stars. As the earth condensed, so the sun condenses. The condensation of the sun from the original nebulous mass can be calculated. Professor Helmholtz gives a formula. Work of condensation= ៖ -g. The mass of the sun is M, the mass of the earth is m; the sun's radius is R, the earth's radius is r. Taking M = 4230 × 1027 lbs., m = 11,920 lbs., R = 2,328,500 feet, and r=20,889,272 feet, we have for the total work performed by gravitation in foot pounds, .r2 M2 Rm The heat, thus produced, would suffice for 20,237,500 years; and the quantity of heat given out, which previously existed as original temperature was 49,000 and 50,000 years' heat; making in all 70,087,500 years' heat. This represents the total amount of heat given out since the mass began to condense. Mr Croll says, "Let us assume that by the time that the mass of the sun had condensed to within the space encircled by the orbit of the planet Mercury (that is, to a space having, say, a radius of 18,000,000 miles) the earth's crust began to form; and let this be the time when the geological history of our globe dates its commencement. The total amount of heat generated by the condensation of the sun's mass from a sphere of this size to its present volume would equal 19,740,000 years' sun-heat. The amount of original heat given out during that time would equal 48,625,000 years' sun-heat, thus giving a total of 68,365,000 years' sun-heat enjoyed by our globe since that period." If the sun's gravity is greatly increased at the centre, the quantity will be consider 1 "Phil. Mag." § 4, vol. xi. p. 76 (1856). Also in "Climate and Time," p. 348 James Croll. 2 "Climate and Time," p. 352: James Croll. ably more; but there is no warrant for anything like the period demanded by some geologists, and the general conclusion arrived at by measurement of the sun's heat is that one hundred millions of years amply suffice for condensation of the nebulous mass into the present form. A process of condensation has not only taken place in the sun, but in all members of the solar system. There has been advance in every one from the gaseous to the liquid, from the liquid to the solid state, to be followed by extinction. There was a time when the sun did not give light in the manner now given,-a time when the earth, even if light were given, could not behold it. There was a time when all the visible glory was invisible, -a time when nature, as now known, was not; so that in a Source beyond nature is nature's origin to be found. Worlds precede worlds in time, as worlds lie beyond worlds in space. Turn to the account:-"God made two great lights, the greater light to rule the day, the lesser light to rule the night. He made the stars also; and God set them in the firmament of the heaven, to give light upon the earth.” The stars seem mentioned lest they should be accounted uncreated. Sun, moon, and stars are classed according to their apparent magnitude and importance. The word "made" is more formative than the word create. It is used for dressing, arranging, making ready. The calf was dressed for Abraham's mysterious visitors, and the cakes were made of meal (Gen. xviii. 6, 7). The same Hebrew word, used for dressing, making, crowning, informs us that the sun was dressed, made, crowned ruler, to give light on the earth. By the time earth and water were separated, and dense vaporous clouds rarified, the earth's mass attained a measure of consolidation, and began to exhibit vital power in lowest forms of vegetable organisms; the sun, clearing the photosphere, sent rays both of light and heat through the vast pressure of his own vapours, and became lord of the day. "Day arises that sweet hour of prime. Thou sun, of this great world both eye and soul, Sun's Physical Constitution. Moon, that now meet'st the orient sun, now fliest ; The Sun's Physical Constitution. 209 The actual density is about one-fourth that of the earth, or a little greater than the density of water.1 The tremendous heat, whatever pressure the gases and vapours are subject to, renders a large solid or liquid nucleus improbable; and we must regard the sun as, in the main, a gaseous body. Around it is no permanent or solid crust but a nearly continuous liquid envelope continually pierced by blasts and jets from within. This great gaseo-liquid mass, swaying our system, is compressed towards the centre, but hardly any definite theories can be adopted concerning its condition. The attractive and repulsive forces are such, the elements exist in forms and quantities with which we are so nearly unacquainted, that when one difficulty is removed from our understanding it gives place to another greater than itself. Possibly, the sun's envelope cannot, in any ordinary sense, be counted a crust at all; but as the vaporous globe is in the presence of the cold of space, there is necessarily a process on the outer surface corresponding to the formation of clouds in our skies. The vapours composing them are chiefly metallic elements, which condensing may descend in sheets of fire, and form a nearly continuous liquid envelope, through which the central imprisoned gases are erupted with great violence. "The sun, according to this view, is a gigantic bubble whose walls are 1 The sun is 1,260,000 times larger than the earth, and 882,000 miles in diameter. More than 1,200,000 earths would be required to form the substance of one sun, and the weight or mass is 300,000 times greater than that of the earth. Our sun is not a large star compared with others, for Sirius is equal in bulk to more than 3000 suns. The surface of the sun is about 2,284,000,000,000 square miles, there are 3,097,600 square yards in every square mile, and on every square yard a heat is produced equal to that which would be caused by burning on it six tons of coal an hour. The impact of matter falling into the sun merely from the earth's distance, would give 6000 times the amount of energy which would be produced by mere burning. The sun travels at the rate of 154,185,000 miles the year. His mean distance from the earth is 91,430,000 miles; rotation on the axis occupies about 25.38 days. gradually thickening, and its diameter diminishing, at a rate determined by its loss of heat. It differs, however, from ordinary bubbles in the fact that its skin is continually penetrated by blasts and jets from within."1 Sir W. Herschel viewed the sun as a solid globe, around which lies an atmosphere of complex nature. He thought that the real body of the sun was neither illuminated nor heated very greatly. "Whatever fanciful poets may say in making the sun the abode of blessed spirits, or angry moralists devise in pointing it out as a fit place for the punishment of the wicked, it does not appear that they had any other foundations than mere opinion and vain surmise; but now I think myself authorised, upon astronomical principles, to propose the sun as an inhabitable world." Sir John Herschel, the son, took a wholly different view as to the coolness of the sun; and, incredible though it seem, regarded certain bright objects, shaped like willow leaves, lying athwart and across each other, as the immediate sources of the solar light and heat. He says, "We cannot refuse to regard them as organisms of some peculiar and amazing kind; and though it may appear too daring to speak of such organisations as partaking of the nature of life, yet we do know that vital action is competent to develope at once heat and life and electricity." The sun's surface has not only spots which have a central part, and a fringe less dark; but also contains certain bright streaks in the neighbourhood of the spots-these by some are called faculæ. "The sun-spots are really hollows or cavities in the solar atmosphere where the temperature of the glowing gases has been reduced."2 The spots are said to be confined to two definite zones, extending about 35° on each side of the equator. The spot zone is a scene of solar tornadoes of whitehot hydrogen, which blow with such fierceness that, compared with these, our most destructive storms are mere summer breezes. The spots are certainly depressions of greater or less depth, and the light received from the umbra of a spot shines through absorbing vapours. "A great difficulty lies in 1 "The Sun a Bubble :" R. A. Proctor. 2 "Spectrum Analysis," p. 263: Henry E. Roscoe. ... Sun's Physical Constitution. 211 the fact that we have no clear evidence to show whether the sun-spots are formed by forces acting from without or from within, . . . whether the seat of that action which leads to the formation of a spot lies below or above the level of the photosphere. . . . As to the prominences, it seems to be demonstrated that some are mere clouds in the upper regions of the solar atmosphere, while others are due to some form of eruption, and only assume the cloud form after the eruption which gave them birth has ceased." There are bridges, arcs, stalks, leaves, and veils of clouds most intricate in structure. The wildest and most fantastic variations take place, renewals of fresh forces with scenes of tremendous tornadoes, swift rushes of glowing vapours and cyclonic motions. The least spot, perceived with the most powerful telescope, must have an area of fifty thousand miles; those visible to the unaided eye must be enormous. The largest spot recorded had a greater breadth than 143,500 miles. We are told the spots sometimes burst in pieces, like a piece of ice dashed on a frozen pool, and disappear in a moment. The eruptions, which occur at all times, are vast explosions, seeming to come from some twenty thousand miles below the edge of the sun's disc, and extending many thousands of miles in every direction. There are brilliant silver copper and ruby-coloured coruscations. Their velocity has been known to exceed two hundred and fifty miles a second. The eruptions are of glowing hydrogen, and other vaporous elements, through an atmosphere of hydrogen. Coloured prominences consist of glowing gas of various tints and forms their origin is still a mystery. The sierra, or rugged line of projections, are ranges of red and other coloured flames, now called the chromosphere. The whole disc of the sun is much marked with roughness like an orange, and some of the lower parts of the inequalities are blackish; the faculæ are ridges of elevation above the rough surface, and sometimes next to a spot will be a protuberant lump of shining matter. Many metals exist in the sun. Gold, silver, platinum, lead, mercury, so far as we know, have not been found. The presence of sodium, calcium, barium, magnesium, iron, chromium, 1 "The Sun," pp. 438, 439: R. A. Proctor. |