SOLAR SOLDERS. 



305 



essence of turpentine; but very soluble in alcohol. 

 It combines with the acids, forming uncrystallizable 

 salts. It is eminently emetic. 



SOLAR (from the Latin sol); any thing belong- 

 ing to the sun. 



SOLAR DAY. See Solar Time. 



SOLAR MICROSCOPE. See Microscope; 

 also Optics. 



SOLAR PARALLAX. See Sun. 



SOLAR SPOTS. See Sun. 



SOLAR SYSTEM. Modern astronomy (see 

 the article Astronomy*), has elevated itself to the 

 notion, that each fixed star is a sun, which we may 

 suppose, according to the law of analogy, accom- 

 panied by a system of planets, so that each star 

 may be the centre of a solar system. But in the 

 narrower and most common sense of the phrase, 

 solar system signifies our sun, with the planets, 

 moons, and comets that revolve round it. The 

 planets are, Mercury, Venus, Earth, with one 

 moon; Mars, Vesta, Juno, Ceres, Pallas, Jupiter, 

 with four moons ; Saturn, with seven ; and lastly 

 Uranus, or Herschel, with six moons already 

 known, and probably others undiscovered. All 

 these planets, accompanied by their moons, move, 

 as do also the comets, in elliptical orbits, round the 

 sun, which is situated in a focus common to all of 

 them, and, by his mighty power of attraction, re- 

 tains them in their orbits. (See Central Forces.} 

 The moons also describe elliptic orbits around the 

 primary planets, with which, at the same time, 

 they revolve around the sun. Moreover, the 

 planets all have a rotation on their own axes, 

 which, together with the inclination of these axes 

 towards the plane of the orbits, and their contin- 

 uance in this situation (parallelism), leads to the 

 idea that all these planets are inhabited by beings 

 endowed with sensation, for whose use these two 

 arrangements seem to have been established. The 

 discoveries of astronomy (e. g. the circumstance, 

 but lately made known by Laplace, that the moons 

 of Jupiter are never all eclipsed at the same time, 

 so that the nights of that planet are never entirely 

 destitute of light) seem to confirm this idea. We 

 can touch upon only a few of the phenomena of our 

 solar system. One of these is the admirable regu- 

 larityin the distribution of the planets in the heavens. 

 Before the discovery of the four new planets 

 Ceres, Vesta, Juno, and Pallas it had been as- 

 certained that the distance of the then known 

 planets from the sun increase according to the 

 following series:--*; 4+3; 4+2-3; 4+16-3; 

 4+32-3; 4+64-3. In this series, amember (4+8-3) 

 was wanting between the members 4+4'3 and 

 4 + 16-3, corresponding to Mars and Jupiter, which 

 circumstance gave rise to the supposition of the 

 existence of an undiscovered planet at the above 

 mentioned distance from the sun a supposition 

 which has been confirmed by the discovery of the 

 four new planets. Another remarkable circum- 

 stance, which indicates a similarity between our 

 earth and the other planets, is the flattening (q.v.) 

 of Jupiter at the poles. The flattening of the 

 earth is ascribed to the original softness of the 

 mass composing it, which yielded to the centrifugal 

 force of rotation. As Jupiter is subject to a very 

 quick rotation, the flattening, supposing this planet 

 also to have consisted originally of a soft mass, 

 would naturally be very great, which late observa- 

 tions have proved to be the case. (For the histori- 

 cal information belonging to this subject, see the 

 article Copernicus and Kepler.') The following ta- 



bular view presents some of the principal points 

 connected with our solar system : 



The circumference of the earth is 25,000 miles. 



" surface 196 000,000 square miles. 



' cubic contents " 170,195,852,l<JOcubicniiles. 



See Laplace's Exposition du Systems du Monde 

 (4th ed., Paris, 1813); Hassenfratz's Cours de Phy- 

 sique Celeste ou Lecons sur I'Exposit. du Systeme du 

 Monde (Paris, 1803, with engravings). A very full 

 tabular view of the solar system is contained in 

 Littrow's Popular Astronomy (in German, Vienna, 

 1825, 2 vols., with engravings). 



SOLAR TIME. The earth revolves, at the 

 same time, on its own axis, and round the sun. 

 During one rotation on its axis it advances about 

 1 in its orbit, and must, therefore, after the com- 

 pletion of a rotation, turn as much more as this ad- 

 vance, before the sun can come again to a given 

 meridian. The time, which, in this way, passes 

 between two successive culminations of the sun, is 

 generally called a solar day. But the rapidity of 

 the earth's advance in its orbit, is different at dif- 

 ferent times : at one period it passes through a 

 larger portion of its orbit in a given time than at 

 others, so that the solar days cannot be equal. 

 Another circumstance, dependent upon the inclina- 

 tion of the axis of the earth to the plane of the 

 ecliptic, is also to be taken into account. The ap- 

 parent solar time, therefore, is distinguished from 

 mean solar time, which has reference to an imagined 

 uniformity, in the progress of the earth round the 

 sun, and supposes the axis of the earth to be per- 

 pendicular to the plane of the ecliptic. Sun-dials 

 show the apparent solar time ; watches, and other 

 time pieces in common use, only the mean solar 

 time. The difference between the two is called 

 equation of time (q. v.) The following table shows 

 what time watches and clocks ought to indicate 

 on the first of every month, when the sun-dial indi- 

 cates twelve o'clock : 



Solar time is to be distinguished from sidereal 

 time. (q. v.) 



SOLDERS consists merely of simple or mixed 

 metals, by which alone metallic bodies can be 

 firmly united with each other. In this respect, it 

 is a general rule, that the solder should always be 

 easier of fusion than the metal intended to be sol- 

 dered by it. Next to this, care must also be taken 

 that the solder be, as far as is possible, of the same 



