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THE GUIDE TO NATURE. 



tan, has a diameter considerably exceed- 

 ing that of the planet Mercury. An- 

 other, Japetus, is of about the same 

 size as our moon. The extreme 

 diameter of the rings of Saturn is 168,- 

 ooo miles, but their thickness does not 

 exceed ioo miles. The mean diameter 

 of the ball of the planet is 73,000 miles, 

 about 13,500 miles less than that of Jupi- 

 ter, but more than nine times greater 

 than that of the earth. It is a curious 

 fact that owing to its slight density which 

 is less than that of water, the force of 

 gravitation upon the surface of Saturn 

 is not very greatly in excess of that upon 

 the earth. Accordingly if we could stand 

 upon Saturn we should not be crushed 

 down by the weight of our own bodies, 

 as we would be upon Jupiter. The 

 slightest mean density of Saturn has led 

 to the conclusion that most of its mass 

 is probably yet in a gaseous state, and it 

 may even give out a slight luminosity of 

 its own. 



Mercury has already been mentioned 

 as an evening star setting very early, at 

 about the same time that Saturn rises. 

 It attains its greatest eastern elongation 

 from the sun on October 4th. Uranus is 

 also an evening star in the constellation 

 Sagittarius, setting about 10 P. M. in the 

 middle of the month. The other planets 

 are all morning stars. Venus at the be- 

 ginning of October is close by the Sickle 

 of Leo on the west, but by the end of the 

 month she will have passed in Virgo, 

 being in conjunction with Jupiter on the 

 night of the nth. Jupiter remains in 

 Leo. Mars is in Virgo, moving east- 

 ward, and will be overtaken by Venus at 

 the end of November. Neptune, very 

 slow in his movements, is in Gemini, and 

 is only visihle in the most powerful tele- 

 scooe. 



The stellar gem of October is the bril- 

 liant Vega in the constellation of Lyra, 

 which may be seen slowly dropping down 

 the northwestern quarter of the sky, 

 preceded by Hercules and the Northern 

 Crown, and followed by the Northern 

 Cross in Cygnus. South of the North- 

 ern Cross, and like it immersed in the 

 Milky Way, glitters Altair in the con- 

 stellation Aquila. The Great Bear, with 

 the Great Dipper, is under the pole in 

 the north, and Cassiopeia is high in the 



east, southeast of Polaris. Below Cassio- 

 peia, toward the south Andromeda lies 

 extended, her head touching the north- 

 east corner of the Great Square of Pega- 

 sus. East of Andromeda, following her 

 along the path of the Milky Way, ap- 

 pears Perseus, brandishing his diamond- 

 hilted sword, and carrying the Head of 

 Medusa, with the strange winking star 

 Algol in his left hand. Near the ecliptic, 

 below Perseus, glitter the Pleiades, just 

 risen, and north of the Pleiades shines 

 Capella, a starry jewel capable of rival- 

 ling Vega itself, but not possessing the 

 blue-white brilliance of the latter. In 

 the east Cetus is seen rising, and, be- 

 tween Cetus and Andromeda appears 

 Aries, the Ram, the first constellation ot 

 the zodiac. Low in the south, east of 

 the meridian, glows the lone star Fomal- 

 haut in the Southern Fish. The Milky 

 Way, now arching across the sky from 

 the northeast to the western horizon, 

 is always an object of great beauty, in 

 the absence of moonlight. It cannot, 

 however, be well seen in cities. Those 

 who have never seen the Milky Way on 

 a clear dark night in the country can 

 have no conception of its sublime beaut)', 

 and of the thoughts of immensity which 

 it awakens. It is very brilliant in Aquila, 

 Cyngus, Cassiopeia and Perseus. Above 

 the head of the Northern Cross the eye 

 readily observes a dark space in it re- 

 calling, to some degree, the appearance 

 of the celebrated '"Coal Sacks" in the 

 Southern Hemisphere. All along its 

 course the Milky Way, composed of mil- 

 lions of stars, too small or too remote 

 to be individually evident to the naked 

 eve, throws itself into vast loops, gar- 

 lands and clouts, which, in their ensem- 

 ble, produce a most majestic effect. A 

 good opera-glass reveals many fields of 

 stars in the Milky Way of astonishing 

 beauty. In the mythologies of many 

 nations the Milky Way has been 

 regarded sometimes as a mysterious 

 pathway among the stars trodden by 

 gods and spirits, and sometimes as a 

 veritable river in the heavens, a river 

 composed of some ethereal fluid as evan- 

 escent as vapor. But in the eyes of the 

 astronomer the Milky Way is the frame- 

 work of the universe, and all modern in- 

 vestigations of the constitution of the 



