68 



THE POPULAR EDUCATOR. 



hunger of the (male) servant. 10. The sou of the physician's brother. 

 11. The woman's servant. 12. To the judge's brother. 13. To a 

 daughter of the American. 14. The past. 15. The men. 16. The 

 Frenchwoman's sisters. 17. To the woman's daughters. 18. The 

 brothers of the (female) servants. 



EXERCISE 2. 



1 . El hombre. 2. La muger. 3. El alma. 4. Las hijas. 5. El 

 hermano del me'dico. 6. El marido de la muger. 7. La hermana del 

 juez. 8. Los liijos del Americano. 9. A los hermanos del me'dico. 



10. A las almas de las criadas. 11. Las hijas de la Francesa. 12. Los 

 criados de los hijos del me'dico. 13. Los maridos de las hijas del juez. 



11. Los hermanos de las criadas. 



EXERCISE 3. 



1. The printers have money. 2. The women are hungry. 3. The 

 painters have books. 4. The judges are thirsty. 5. The women gave 

 books to the Frenchwoman's father. 6. The men gave money to the 

 American's mother. 7. The carpenters went to the painter's house. 

 8. The judges wrote letters to the painter's mother. 9. The ship- 

 carpenters have money. 



EXERCISE 4. 



1. Los pintores tienen dinero. 2. Las mngeres tienen maridos. 

 3. Los carpinteros dieroa un libro al hijo del juez. 4. Las hijas de la 

 Francesa escribieron cartas a los hijos del - juez. 5. El me'dico escri- 

 bieron carttis a la madre del pintor. 6. Los criados del medico escri- 

 bieron cartas a las criadas de la Francesa. 7. Los impresores f ueron 

 casa del juez. 8. Los caballos tisnen hambre. 9. Los bueys tienen 

 sed. 



LESSONS IN ASTRONOMY. X. 



THE PLANETS (continued) MERCURY -VENUS THE EARTH. 



MERCURY, represented by the symbol 5, has been known almost 

 from the earliest ages. This speaks well for the skill of early 

 astronomers ; for, owing to its small size and proximity to the 

 sun, it is very difficult to obtain 

 a satisfactory observation of the 

 planet. It is said that Copernicus 

 even, though the greater part of his 

 life was devoted to the study of the 

 heavens, never once succeeded in 

 obtaining a view of this orb. The 

 greatest distance it can ever be from 

 the sun is about 29, and sometimes 

 its elongation before it begins to 

 return is not more than 16 4. Fig. 

 19 will serve to explain this fact, 

 and the apparent motion of the in- 

 ferior planets generally. In it M re- 

 presents the Earth travelling along 

 in its orbit P O, while A B C D repre- 

 sents the orbit of Mercury, the sun, 

 s, being the common centre of both. 

 When the planet is approaching 

 the part B of its 01 bit, it will for a 

 short time appear to be almost sta- 

 tionary, and then will travel in the 

 same direction as the sun from B 

 to A with a gradually increasing 

 speed, which at A begins to de- 

 crease, till at D it again becomes 

 stationary. As it still travels on 

 in its course from D to c, and 

 thence to B, it will appear to be 



moving in the contrary direction ; thus it will be seen that at 

 times it is stationary, while sometimes its motion is direct, 

 and sometimes retrograde. The greatest elongation it can 

 obtain is manifestly half the angle E M L. When situated to 

 the west of the sun, the planet rises a little time before it, and 

 is a morning star ; when, however, it is on the east, it -is an 

 evening star, being visible for an hour or two after sunset. At 

 C the planet is said to be in inferior conjunction, and at this 

 period a transit may take place. As, however, the orbits of 

 Mercury and the earth are not in the same plane, the planet 

 will frequently be above or below the sun, and no transit will 

 then occur. 



The orbit of the planet must, howevsr.% obviously cross the 

 plane of the ecliptic in two points, and these points are called 

 the nodes, the ascending node being that at which the planet 

 passes from the south to the north side of the equator, and the 



Fig. 19. 



descending node that at which it passes from north to south. 

 A transit, then, will occur whenever the planet is in one of ita 

 nodes at tho time of its inferior conjunction. The next time 

 that this will happen will be on May 6th, 1878. 



As the planets are not self-luminous, but shine by light re- 

 flected from the sun, the inferior ones will be found to exhibit 

 phases corresponding to those of the moon. The period of 

 their greatest brightness is not, however, when they present 

 a full disc, for then they are in superior conjunction, and there- 

 fore at their greatest distance from the sun, besides which they 

 are almost or quite hidden by its rays. 



The mean distance of Mercury from the sun is nearly 

 35,393,000 miles. Tho eccentricity of its orbit is, however, 

 very great, so that its distance varies between 28,000,000 and. 

 43,000,000 miles. It performs its journey round the sun in 

 a trifle over 87 days, so that its year is less than a fourth the 

 length of ours. Its speed in its orbit is very great, being far- 

 beyond that of any of the other planets ; hence, in the old 

 mythology, Mercury was represented with wings to his feet. 



The planet is but small, its diameter being reckoned at 2,960 

 miles, or rather more than one-third that of the earth. Its 

 period of rotation on its axis is 24 hours 5| minutes, and thus 

 it closely resembles the earth in this respect. 



This next planet in order of distance from the sun is Venus', 

 represented by the symbol ?. This planet has been known 

 from remote antiquity, and was, in all probability, the first 

 discovered, as it is, at those periods when most favourably 

 situated, the brightest of them all. So brightly, indeed, does it 

 shine at times that it is visible during the day, and casts a 

 shadow at night. Its apparent size and brilliancy vary, however, 

 very greatly, as will be easily understood if we remember that 

 when in inferior conjunction it is 

 within about 25.000,000 miles of 

 the earth, while when it is in 

 superior conjunction this distance 

 is increased by the diameter of 

 Venus's orbit, and becomes nearly 

 100,000,000 miles. 



Fig. 20 will explain this, and at 

 the same time convey a good gene- 

 ral idea of the phases of an inferior 

 planet. When in the part A of its 

 orbit, directly between the earth 

 and the sun that is, in inferior con- 

 junction it is at its least distance^ 

 from us, and hence would appear 

 most brilliant if it were luminous. 

 As, however, it only shines by re- 

 flected light, and its dark side is- 

 turned towards us, it is invisible. 

 Besides this, it appears so close to 

 the sun as to be lost in its bright- 

 ness, unless it should happen to 

 pass across the sun's disc, where 

 it appears as a round black spot. 

 As it now travels onward towards 

 B, it gets further and further re- 

 moved to the west of the sun, and 

 thus rises earlier and earlier, being- 

 then known as Lucifer, or the 



Morning Star. At the same time its bright hemisphere becomes 

 partly turned towards the earth. When exactly half illuminated, 

 as at B, it is at its greatest elongation from the sun, being- 

 distant about 48. Its period of greatest brilliancy, however, is a, 

 little before this, when about one-third of its disc is illuminated. 

 Having attained its greatest elongation, it is stationary for a 

 short time, and then begins to return towards the sun ; an in- 

 creasing portion of the disc being illuminated, though on account 

 of its increasing distance it appears smaller. It is then lost 

 again in the sun's rays for a time, and when it re-appears to the 

 east of the sun, it does not rise till after that luminary, and 

 therefore is no longer the Morning Star. It remains, however, 

 visible for some time after sunset, and is known as Hesperus, 

 or the Evening Star. After attaining its greatest eastern elon- 

 gation at D, it returns to A to go through the same phases again. 

 These phases are not visible to the naked eye, and hence the 





