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more were found ; accordingly it was believed that all had been 

 discovered, and that these four Ceres, Pallas, Juno, and Vesta 

 were the four fragments of a large planet which had once re- 

 volved in an orbit nearly resembling theirs. These planets are 

 sometimes distinguished by the signs ? , ? . J > & 



At the close of the year 1845 the discovery of a new asteroid 

 was announced by Hencke, and again attracted the attention of 

 astronomers to the subject. Many new observers now entered 

 upon the task of trying to discover some more of these minute 

 bodies, and since that time few years have passed without adding 

 fresh planets to the list, which at present contains more than 

 100. When it is remembered that these planets are all very 

 small, many of them being less than fifty miles in diameter, it 

 will be seen that this is a difficult task. They do not present 

 a defined disc in the telescope, as the larger planets do, but 

 merely appear like minute stars of about the twelfth magnitude, 

 BO that the only way of observing them is by accurately noting 

 down all the stars visible in a given small portion of the 

 heavens, and then carefully watching on successive evenings to 

 ascertain if any of these appear to have changed their positions, 

 or if any fresh points of light appear among them. 



It was soon found that, with so many planets, symbols to dis- 

 tinguish each would lead to almost inextricable confusion. All 

 the minor planets are, therefore, now distinguished by a num- 

 ber enclosed in a circle, thus, Ceres 0, Pallas ; and the four 

 signs given above are seldom employed. 



The names of many of the heathen goddesses have been used 

 to distinguish these planets. A list of most of these will be 

 found in Vol. II., p. 45. 



Three only of these planets have been seen by the naked eye, 

 namely, Vesta, Ceres, and Pallas ; and it is only under very 

 favourable circumstances that they can thus bo seen. The dia- 

 meter of Vesta and Ceres is about 228 miles. Pallas, ac- 

 cording to some observers, is larger ; others, however, make it 

 less. All the rest are smaller than these. Their distances from 

 the sun vary very considerably, the nearest, Flora , having a 

 mean distance of 201,000,000 miles, while the farthest, Maxi- 

 nailiana (55), is distant about 313,000,000 miles. Their times of 

 revolution are likewise very different, the two planets just named 

 taking 3 - 266 and 6'413 years respectively to complete their orbits. 



Another remarkable feature in connection with this group of 

 planets is the great eccentricity of many of their orbits. This, 

 with many other facts in connection with them, is in favour 

 of Gibers' fanciful theory, that we have here the remains of a 

 single large planet. If we trace out all their orbits, we can find 

 one point near to which most of them pass, and the force which 

 scattered them would fully account for any deviation of others 

 from this spot. Their orbits, likewise, are very much interlaced, 

 so that it has been said that, if they were represented by rings, 

 any one of these, on being lifted, would raise all the rest with it. 



Some of these bodies when carefully watched are found to 

 exhibit very remarkable changes in brilliancy, suddenly increas- 

 ing, and then after a brief interval fading again as rapidly. The 

 apparent explanation of this is, that they have very irregular 

 shapes, as they would have were they fragments of a large planet, 

 and that hence, as they rotate, the amount of light reflected 

 from their surfaces varies very greatly. Owing to their small size 

 very little is known of the nature of these bodies : traces of an 

 atmosphere have, however, been discovered around some of them, 

 that around Pallas appearing to have great density. 



JUPITER. 



Beyond this group of fragmentary bodies, lies the largest 

 member of our system, the planet Jupiter, represented by the 

 sign V. The equatorial diameter of this orb is 85,390 miles, 

 or more than ten times as great as that of the Earth; hence, 

 it at once exhibits a distinct disc, even in a telescope of low 

 power. When in opposition, it shines with a brilliancy nearly 

 equal to that of Venus, and has been known to cast a sensible 

 shadow. It is at all times distinctly visible to the naked eye, 

 except when overpowered by the brilliancy of the solar rays, 

 and hence it has been known from the earliest ages. 



Its mean distance from the sun is 475,693,000 miles, and it 

 completes its journey round this orbit in 4332'58 days, or a few 

 weeks less than twelve of our years. Its speed in its orbit is 

 considerably less than half that of the Earth : we always find, 

 however, that the further the planets are removed from the sun, 

 the less is the speed at which they move, 



The plane of Jupiter's orbit is inclined very slightly to that 

 of the ecliptic, and hence there is a difficulty in ascertaining the 

 exact points in which they intersect, and in determining the 

 length of its years in the usual way. This is, however, easily 

 overcome by ascertaining its synodic period, which is nearly 

 399 days, and calculating from this its sidereal period. 



When examining this planet with a telescope, the first thing 

 that strikes us is the fact that it is accompanied by four 

 satellites or moons. Three of these were discovered on 

 January 8th, 1610, by Galileo, when he first directed his tele- 

 scope towards the planet, and the fourth a few evenings later. 

 A very low power such as that afforded by an ordinary opera- 

 glass suffices to show them all distinctly. It is even said that 

 at times they have been seen by the unaided eye. 



These satellites revolve around Jupiter in orbits which are 

 almost circular, and veiy slightly inclined to the plane of the 

 planet's equator. Owing to this latter fact, the three nearer ones 

 are eclipsed every revolution, and the outer one in nearly every 

 revolution, so that the phenomena of eclipses must be far from 

 rare to the inhabitants of this planet, there being about 4,500 

 lunar eclipses, and about the same number of solar ones in one 

 Jovian year. 



The eclipses and transits of these bodies are very interesting 

 phenomena, and may be easily observed with an ordinary 

 telescope. A full list of them is given in the Nautical Almanack 

 for each year, and scarcely a day passes without some being 

 observed ; they are frequently used in determining the longitude 

 of any station of observation. When one of the satellites 

 passes between the Earth and the planet, it is seen in transit as 

 a bright spot on its face ; its shadow is also seen as a dark spot 

 at a little distance from it, presenting the appearance of two 

 satellites in transit. It was by observing these eclipses that the 

 speed of light was first ascertained. It was found that the time 

 of the occurrence of these eclipses differed from that predicted, 

 being sometimes as much as eight minutes sooner, and at times 

 as much later. This led to inquiry, and Von Eomer at length 

 noticed that when Jupiter was in the part of its orbit most 

 remote from the Earth, the eclipses occurred later than the 

 predicted time, while when it was in perigee they were earlier, 

 and hence he started the conjecture that the discrepancy 

 might be accounted for by supposing that light took sixteea 

 minutes to travel across the Earth's orbit. Subsequent investi- 

 gation has proved that this theory was the true one. 



The annexed table gives us the more important facts about 

 these satellites : 



Name. Mean Distance. Sidereal Period. Diameter. 



lo 267,380 miles. Id. 18h. 27m. 2,252 miles. 



Europa 425,160 3 13 14 2,099 



Ganymede 678,390 7 3 43 3,436 



Callisto 1,192,820 16 16 32 2,929 



From this it will be seen that the appearance of the Jovian 

 sky must be very remarkable, especially as all the moons perform 

 their journey round the planet in a very short time, and hence 

 their changes are very rapid. 



IESSONS IN ENGLISH. XLVII. 



COMPOUND PEONOUNS ADJECTIVE PEONOUNS. 



THE pronouns of which we have just treated are simple pro- 

 nouns. Of these simple pronouns others are formed, which, as 

 consisting of more than one word, are termed compound pro- 

 nouns. 



The reflective pronoun is compound, and having for its root 

 the old word self (German selbst, same) is inflected thus : : 

 1st Person. 2nd Person. 3rd Pe?-son. 



SINQ. Myself. Thyself. Himself. 



FLUB. Ourselves. Yourselves. Themselves. 



For the sake of distinction and emphasis, the nominative of 

 the personal pronoun may be prefixed, thus : 



1st Person. 2nd Person. 3rd Person. 



SINO. I myself. Thou thyself. They themselves. 



PLUB. We ourselves. Tou yourselves. He himself. 



The use of these pronouns will be understood better from an 

 example or two : for example : 



I struck myself; I will go myself; I myself said it. He hurt himself t 

 he has gone himself; he himself made the remark. 



