MEKCUBY VENUS THE EARTH. 67 



restore the day." As an image of the anticipated dawn of full mental illumination, the 

 sacred writers introduce the day-star ; and it occurs as an emblem of mere human glory 

 in the ode on the overthrow of the King of Babylon : 



" How art thou fallen from heaven, O Lucifer, son of the morning!" 



Homer compares the son of Hector to the star that gilds the morn, and the point of 

 the spear of Achilles to the keen light of radiant Hesper. Men of all ages, climes, and 

 ranks, from the shepherd boy to the grave philosopher, have turned with interest and 

 delight to this planet ; and whether examined as a telescopic object, or contemplated with 

 the unassisted sight, it is an inexpressibly lovely orb, and one that will always excite 

 admiration. 



Venus is situated in the system at a mean distance of sixty-eight millions of miles 

 from the sun, through which she would fall in thirty -nine days and a half, if surrendered 

 solely to the attraction of his mass. Her periodical revolution is accomplished in 224f 

 days, involving a velocity of 80,000 miles an hour. The planet is rather smaller than 

 our own globe, having a diameter of 7700 miles. She rotates upon her axis in about 

 23^- hours. Venus exhibits alternately a fine thin crescent and a semicircle like the 

 moon, but she can scarcely be seen quite full, because when the whole of her enlightened 

 hemisphere is turned towards us, she is either behind the sun or so near him as to be hid 

 by the splendour of his light. The diagram represents the various appearances of the 

 planet as she moves in her orbit, in the order of the letters. 



Superior conjunction. 



East elongation, f} W S^W (U West elongation. 



t " 



a 6 



Inferior conjunction. 



We first behold Venus as a morning star for a short time before sunrise, soon after 

 passing between the earth and the sun at her inferior conjunction, when she appears 

 crescent-shaped as seen through a telescope. She continues gradually to gain upon the 

 sun, rising earlier and earlier, until her greatest angular distance westward has been 

 attained, when she exhibits a semicircle, and shines with great splendour. Then the 

 planet begins to return towards the luminary, making the same daily progress as in 

 separating from him, rising later and later, diminishing also in brilliance, owing to the 

 overpowering solar glory, in which she is lost at the time of her superior conjunction, 

 being then behind the sun in relation to us. A few days afterwards Venus becomes an 

 evening star, and is seen a short time east of the sun after his setting. She soon seems 

 to have fallen considerably behind him, and continues to depart farther and farther, 

 setting later every night, until her greatest elongation eastward has been reached, when 

 she again exhibits a bright semicircle. The course towards the sun is then resumed, 

 until she comes between him and the earth, sets with him, and is invisible, owing to the 

 whole of her enlightened side being turned away from us. In a few days the phenomena 

 of the morning star are repeated. Venus is seen to keep on the same side of the sun for 

 a period of about two hundred and* ninety days together. This seems at first sight a 

 singular anomaly, as it is a greater interval than that occupied by an entire circuit round 

 him It is however at once accounted for by considering that the earth is proceeding at 



