xxxvi INTRODUCTION TO ASTRONOMY. 



Venus, the next in the order of planets, is 68 millions of miles from the 

 sun ; she revolves about her axis in 23 hours and 21 minutes, and goes 

 round the sun in 224 days 17 hours. The diameter of Venus is 7,687 

 miles. The orbit of Venus is within ours ; during 1 nearly one-half of 

 her course in it we see her before sunrise, and she is called the morning- 

 star ; in the corresponding part of her orbit, on the other side, she rises 

 later than the sun. We then cannot see her rising, as she rises in the 

 daytime ; but she also sets later ; so that we perceive her approaching the 

 horizon after sunset : she is then called Hesperus, or the evening-star. i 



The planet next to Venus is the Earth, of which we shall soon speak at 

 full length 5 at present we shall only observe, that we are 95 millions of 

 miles distant from the sun that we perform our annual revolution in 

 365 days, 5 hours, and 49 minutes and are attended in our course by a 

 single moon. 



Then follows Mars. He can never come between us and the sun, like 

 Mercury and Venus j his motion is, however, very perceptible, as he may 

 be traced to different situations in the heavens ; his distance from the sun 

 is 144 millions of miles ; he turns on his axis in 24 hours and 39 minutes ; 

 and he performs his annual revolution in about 687 of our days : his 

 diameter is 4,189 miles. Then follow four very small planets Juno, 

 Ceres, Pallas, and Vesta, which have been recently discovered, but whose 

 dimensions and distances from the sun have not been very accurately 

 ascertained. 



Jupiter is next in order. This is the largest of all the planets ; he is 

 about 490 millions of miles distant from the sun, and completes his annual 

 period in nearly twelve of our years ; he revolves on his axis in about ten 

 hours ; he is above 1,400 times as large as our earth, his diameter being 

 89,170 miles. The respective proportions of the planets cannot therefore, 

 you see, be conveniently delineated in a diagram. He is attended by 

 four moons. 



The next planet is Saturn, whose distance from the sun is about 900 

 millions of miles. His diurnal rotation is performed in ten hours and a 

 quarter ; his annual revolution in nearly thirty of our years ; his dia- 

 meter is 79,000 miles. This planet is surrounded by a luminous ring, the 

 nature of which astronomers are much at a loss to conjecture : he has 

 seven moons. 



Lastly, we observe the Georgium Siclus, discovered by Dr. Herschel, 

 and which is attended by six moons. His numerous moons are, however, 

 far from making so splendid an appearance as ours ; for they can reflect 

 only the light which they receive from the sun ; and both light and heat 

 decrease in the same ratio or proportion to the distances as gravity ; 

 consequently Saturn, which is at nearly ten times the distance at which 

 we are from the sun, has a hundred times less heat and light. To us 

 such a climate would not be habitable ; but this furnishes no argument 

 against the supposition that these planets are worlds, peopled with beings 

 whose bodies are adapted to the various temperatures and elements in 

 which they are situated. Whether we judge from the analogy of our own 

 earth, or from that of the great and universal beneficence of Providence, 

 we may reasonably conjecture this to be the case : and an inhabitant of 

 Mercury might with as much plausibility pity us for the intense coldness 

 of our situation, or those of Jupiter and Saturn for our intolerable heat, 

 as we can draw any inferences against their existence, from the circum- 

 stance that we, constituted as we are, could not live there. 



Comets are supposed to be planets. The re-appearance of some of 



