96 



VENUS. 



llie mean distance of thirty seven millions of miles, and com-  

 pletes his revolution in about three months. According to Sir ^ 

 Isaac Newton, the heat and light of the sun on the surface \ 

 of Mercury, are almost seven times as intense as on the sur- ; 

 face of the earth in the middle of summer ; which, as he ; 

 found by experiments made for that purpose with a ther- i 

 mometer, is sufficient to make water fly off in steam and va- i 

 poui. Such a degree" of heat, therefore, must render Mer- 

 cury uninhabitable to creatures of our constitution ; and if  

 bodies on its surface be not inflamed and set on fire, it must ^ 

 be because their degree of density is proportionably greater j 

 than that of such bodies is with us. When Mercury passes ^ 

 over the sun's face, or is between us and the sun, this is : 

 called his transit, and the planet appears like a black spot in 1 

 the sun's disk. The light emitted by Mercury is a very \ 

 bright white. I 



Fair Venus next fulfils her larger round, : 



With softer beams, and milder glory crowned ; 

 Friend to mankind, she glitters from afar, ; 



Now the bright evening, now the morning star. 



Baker. 



Venus is computed to be sixty-eight millions of miles i 

 from the sun, and completes her annual rotation in about ] 

 seven and a half months, turning on her axis in a little less ;! 

 than twenty four hours. The light, which this planet re- ] 

 fleets, is very brilliant, and often renders her visible to the ; 

 naked eye in the day-time. When Venus is to the west of ■] 

 the sun, she rises before the sun, and is called the morning ^ 

 star ; when she appears to the east oi* the sun, siie shines in ^ 

 the evening, and is then called the evening star. She is in i 

 each situation alternately, for about two hundred and ninety ] 

 days ; and, during the whole of her revolution, she appears, 

 through a telescope, to have all the various shapes and ap- 

 pearances of the moon. As the orbit of Venus is within , 

 that of the earth, like Mercury, she sometimes passes over the 

 sun's face, and her transits have been applied to one of the 

 most important problems in astronomy, — that of determining 

 the true distances of the planets from the sun. The atmo- 

 sphere of Venus has been calculated to be fifty miles high ; 

 this has been learned from observing her transits, when her 

 Etmosphere was seen to throw a shade on the sun's disk h 



