$22 SCIENTIFIC RECREATIONS. 



upon the planet, must appear about seven times larger than he does to us. 

 Mercury's year is about eighty-five days in length, so the seasons must be 

 shorter if they follow the same rotation as ours. It passes through space 

 with an exceedingly rapid motion, and so probably the ancients called the 

 swift planet Mercury after the winged messenger of Jove. 



Mercury is not an easy planet to observe, owing to its proximity to 

 the sun, yet the ancients managed to descry it. But it can be seen just 

 before sunrise and sunset in autumn, and in spring if the weather be clear. 

 It possesses phases similar to our moon. Some authorities have stated that 

 Mercury has an atmosphere, but this circumstance, as well as its formation, 

 is still shrouded in mystery. Mercury's day is a few minutes longer than 

 ours. 



A transit of Mercury is represented in the accompanying illustration 

 (fig. 577). This phenomenon took place in 1845, but there have been many 



Fig. 577. Transit of Mercury. 



others noticed. The first recorded took place in November 1631, and these 

 transits always occur in May or November. 



VENUS. 



VENUS is the planet next in order, and revolves about 66,000,000 of 

 miles from the sun. It is the nearest planet to the earth, and is somewhat 



smaller than the latter. This planet 

 is both a morning and evening star, 

 and is very brilliant so much so, that 

 any close observation with the tele- 

 sope is not possible ; and when at 

 her nearest point she is invisible as 

 Fig. 5 7 8.-Orbit of Venus. she passes between us and the sun, 



and of course when fully illuminated she is directly beyond the sun, and 

 enclosed in his rays. But under other circumstances she is distinctly visible 

 as a crescent in the evening, and nearly full as a morning star. Venus 

 goes round the sun in 224 days, and her day is rather less than ours. 



Venus has long been celebrated as the morning and evening star, as 

 " Lucifer " and " Hesperus." " Lucifer, son of the morning," is mentioned 

 by Isaiah. That Venus possesses an atmosphere denser than our own can 

 scarcely be doubted. The observations made during the successive transits, 

 particularly the last (1874), seem to have established the fact that aqueous 



