2382 SOLAR PARALLAX-SOLDER are thence reflected upon the back of the object, and diverge on the system of lenses at the mouth, which form the image. Instead of the sun's rays the oxyhydrogen lime-light and the electric light have been employed. Solar Parallax, Solar Spectrum, Solar Corona, etc. See under head of SUN. Solar Sys'tem consists of the sun with its eight orin- or hyperbolic orbits (mostly Sun as seen from Mercury. such) can be considered as Sun as seen Sun as seen Sun as seen from Mars. Bun as seen from volve in approximately the same planes and in the same di rection as their primary planets. The asteroids are not quite so regular. The range of the eccentricities and inclinations of their orbits is considerably greater, but they are all confined within the belt between Mars and Jupiter, and they revolve in the same direction as all the large planets. This unquestionably is not the result of chance, which would be more nearly represented by the distribution of the orbits of comets, but it points to some community of origin, which is usually explained by what, in some one of its various forms, is called the NEBULAR HYPOTHESIS, (q. v.) Stability.-The sun and its eight large planets are essentially a stable sys tem. All the ELEMENTS (q. v.) of the planetary orbits, with the exception of their mean distances from the sun, are undergoing, it is true, constant change. But these changes are periodic in their character, and, after various periods of time, some of them of immense duration, they all return to essentially the same values. Some of the asteroid orbits, however, on account of their great eccentricities and inclinations, may not be stable, but they can hardly interfere in any way with the rest of the solar system. Elements.-The principal elements of the solar system are given in the following table. For a more particular description of each of the planets, and of their satellite systems where they have such, look under the name of each planet. Motion in Space.-Systematic discussion of the proper motions of a large number of stars has shown that the sun with its attendant planets is moving swiftly through space toward a point in the constellation Hercules whose right ascension is about 267°, and its declination about +31°. The various determinations of this direction agree fairly well, but the actual rate of motion depends upon what assumptions are made as to the average distances of the stars employed in the discussions, and this, until much more work is done in the determinations of stellar parallax, must be largely conjecture. With the perfection of the methods of determining the motions of stars in the line of sight, (see MOTION IN THE LINE OF SIGHT,) we may expect that this uncertainty will eventually be banished, and that we shall know the speed as well as the direction of the motion of our system through space. The point toward which we are moving is sometimes called the "apex of the sun's way," or perhaps better, adopting the notation suggested by Prof. Newton in connection with the direction of the earth's motion and meteor radiants, we may call the point that we are approaching the "sun's goal," and the opposite point which we are leaving the "sun's quit." having only a temporary from Venus. connection with the solar system. To these should be added the meteor streams, (see METEORS,) whose existence is from time to time made known by the earth's near approach to some part of each of them, and a probably countless number of similar streams which will never be known to us on account of the distance of all their parts from the earth's orbit, except as the perturbations of the planets may Sun as seen from Juno. bring a few of them within striking distance as ages roll by. The ZODIACAL LIGHT Sun as seen from (q. v.) is also a part of the solar system, though little is actually known of its constitution. Symmetry. If we confine our attention for a moment to the sun and Solder, an easily fusible alloy used for joining metals. its eight larger planets Ss. are of various kinds, suited to different metals. They we find a remarkable symalways require to be used with a flux, such as borax, resin, metry in their relations. The chloride of zinc, sal-ammoniac, etc. The following are the planetary orbits are all nearprincipal Ss.: Pewterers' S.-bismuth 2 parts, lead 4 parts, ly circular and nearly in one tin 3 parts. Plumbers' S. for coarse work-tin 1 part, lead plane, approximately the 3 parts. For finer work-tin 2 parts, lead 1 part. Spelter plane of the rotation of the sun itself. They all revolve in S.-12 parts zinc to 16 parts of copper. Soft spelter S. the same direction, likewise that of the sun's rotation. With-equal parts of copper and zinc. When Ss. are applied in PRINCIPAL ELEMENTS OF THE SOLAR SYSTEM. Ceres. Sun as seen from Pallas. Sun as seen from Reen Sun Saturn. from Uranus. Sun as seen from Neptune. Relative size of the Sun as seen from different planets. N48 4.03 14.7 4.39 17.1 65. 85. 1.22 0.91 0.88 the exception of Uranus and Neptune (probably) the planes | the common work of plumbers and tinmen, a tool called the of rotation of the planets approximately coincide with those of their orbits, and their direction is the same as the common direction of revolution. The satellites of the planets all re soldering-iron is used; this is made red hot and forms a convenient means of applying fire direct to the S. and flux. Although called the soldering-iron, the portion of the tool to be |