every human being now existing in the world, commenced visible existence as a minute ovum or embryo, which has been gradually built up to the dimensions of maturity by atom joined to atom. 316 Speculation as to the Origin of the Solar System. It is known that all the elementary substances of which larger masses in the world are formed, namely, the metals, carbon, sulphur, and the rest, are resolvable by strong heat into a gaseous or aëriform condition, invisible to human sight; so that this solid globe, and all within and upon it, might, by heat, be changed into a vast transparent mass. We may adduce as illustration of this truth the phe nomena now to be described. Any person looking up into a perfectly transparent sky, may see there nought but bluish space or extension, although aware that the space is occupied by a material atmosphere. A change then occurring in the temperature, or electrical state of that atmosphere, may suddenly cause a haze to appear. The moist particles of the haze may then multiply and become a dense cloud, and that moisture may soon condense, or coalesce, into drops of rain; these, with increase of cold, may be frozen into solid snow-flakes or hail-stones, which mutually cohering into larger masses, and descending with violence to the ground, can demolish any fragile objects, and may even kill animals of considerable size. If the atmosphere during such changes have a vorticose motion as in the whirlwind or cyclone, the solid masses must share in such motion. If something like this solidification of gaseous invisible matter had occurred long ago on a prodigiously larger scale, planets instead of hail-stones might have resulted, and the present solar system might have come to occupy the space previously held by the transparent cloud. Such a supposition would seem to explain why all the planets, and all the satellites about the planets, revolve in the same direction, and why the individual planets, and even the sun himself, rotate about their own centres in that direction, and further, it accounts for the very remarkable fact that in the wide space between the two planets Mars and Jupiter, where, to maintain uniformity of condensation throughout the space, a larger planet should have appeared, but did not, the improved telescopes of modern times discover a great number of smaller masses revolving, which, if united, would form such a planet as seemed due to the situation. 1050. This sketch is presented, not as the history of the origin of the solar system, but, by analogy, as a familiar type, in order to facilitate the conception of the great facts really existing. The invention of the telescope and other valuable means of observing facts, and the improved modes of computation devised in recent times, are by no means opposed to some such origin of the solar system as that above sketched. Numerical Elements of the Solar System. 817 Table of the great bodies of the Solar system, with their sizes, distances, and other particulars. In thinking of the stupendous magnitudes and relative distances of the bodies which constitute our solar system, it facilitates the conception to figure before the mind an arrangement exhibiting nearly the like proportions on a vastly smaller scale, among known things. Thus, if a Londoner imagines a globe, of about eighty feet in diameter, placed on the summit of St. Paul's Cathedral, to represent the sun, the comparative distances and magnitudes of the planets would be roughly as follows :-— Mercury, a globe of 5 inches diameter at Putney. It is a matter of pure arithmetical computation that a railway train at a uniform speed of forty miles an hour would need nine months to reach the moon, three hundred years to reach the sun, and a thousand times as much to reach the nearest fixed star. One is surprised to think how small a portion of the space of the universe is occupied by the substance of the sun and the worlds around him. THE SOLAR SYSTEM. The Sun. 1051. The Sun, the central attracting body of the solar system, and the source of heat and light to all its members, is a vast globe. It exceeds the earth in diameter more than one hundred times; in volume, a million and a quarter times; and, in mass, nearly onethird of a million of times.* The reason why the mass is comparatively less than the volume is, that the density or specific gravity of the sun is only one-fourth of the earth's density. Still the mass of the sun exceeds by six hundred and fifty times the mass of all the planets taken together. The sun rotates on its axis like the earth; each revolution takes twenty-five days. The intensely brilliant surface has long been known to contain dark patches or spots. These do not remain constant-they come and go. They may be very numerous, and they may be very large. One was observed by Sir W. Herschell whose diameter exceeded fifty thousand miles.† Around the dark spots, and in other places, there are brighter streaky portions called facula. These also are constantly changing their shape. The spots are generally seen to consist of a dark central part or nucleus, called the umbra, and a less dark surrounding fringe, called the penumbra. Their forms are very irregular. They are all subject to one steady change of position and appearance, which has been interpreted as due to the rotation of the sun, and was the means of discovering and estimating that rotation. The changes in their own nature relate to the manner of their appearance and disappearance, which are both gradual; the umbra and the pen. umbra increasing and diminishing together. * The enormous size of the sun may be estimated from this fact. One half of its diameter (426,450 miles) would be nearly equal to twice the distance of the moon from the earth. †The spots were first discovered by Galileo in 1610. The Solar Atmosphere. 819 It is found that the sun's surface passes through a regular period of spot-development, from the extreme of total absence of spots, to the extreme of maximum abundance. This period is about eleven years. The spots are undoubtedly associated with magnetic disturbances in the Earth. Likewise, they seem to vary with the positions of the planets Mercury, Venus, the Earth, and Jupiter. Some other singular features connected with the sun's disc have of late years been observed when the sun is under a total eclipse. At the moment of totality there is seen around the sun a vast halo of silver-bright light. It has a radiated structure, and extends to a great distance, sometimes as far as the breadth of the moon's diameter. These are in addition to rays called aigrettes, that seem to shine through the continuous halo. This halo has been designated the corona. Besides the corona itself, with the aigrettes, there have been observed, close to the edge of the moon, and within the corona, peculiar red prominences of various and fantastic shapes. They are very numerous, and arc classified into jets-single, grouped, and ramified; columns or pyramids; and cloudy waves. These are named prominences or protuberances. Like the spots, they come and go; and from their magnitude and rate of change, indicate matter in motion at an enormous velocity. 1052. Such is a brief outline of the solar peculiarities. Their expla nation, so far as yet made out, is connected with the general view now taken of the sun's exterior. The body or mass of the sun is believed to be a comparatively dark solid; on this floats an immense ocean of fluid matter, which contains the light-giving ingredients—the luminosity being connected with the enormously high temperature of the sun's surface and body. The ocean, or atmosphere, or fluid environment of the sun, has been distinguished into several parts or layers. Chief of these is the more exclusively luminous layer, called the photosphere, or the light-surface or shell. This is a mass, perhaps thousands of miles in depth, of intensely heated matter: it is the solar surface as we see it, and the chief source of both light and heat. The spots are breaks or openings in this luminous stratum, through which is seen the darker surface of the sun. Being fluid, and exceedingly hot, it is believed to be in a state of incessant agitation, so as now and then to open up and leave comparative darkness for a time; the opening and the closing being very rapid, although gradual. The white-hot material of the photosphere does not exhaust the |