MAES PLANETOIDS JUPITER SATURN URANUS NEPTUNE. 



95 



caused by great physical convulsions. A far more probable and generally received opinion 

 is, that the dark bands are the actual body of the planet, and the bright bands compact 

 and undisturbed strata of clouds and vapour. It is also supposed that currents similar 

 to our trade winds set in from the poles 

 to the equator of Jupiter, which assume a 

 parallel direction as the equator is ap 

 proached, owing to the prodigious ve 

 locity of his equatorial regions, and 

 thereby cause those parallel aggregations 

 of vapour, through the interstices of 

 which the opaque body of the planet is 

 seen. Of course, this explanation is 

 purely hypothetical, but it is the best 

 that has been offered. Admitting the 

 explanation, it follows that Jupiter has 

 clouds, rain, wind, water, evaporation, 

 and seems thus fitted up to be the ha 

 bitation of vegetable productions and 

 animal life. 



The discovery of the moons of Jupiter, 

 four in number, was one of the first-fruits 

 gathered from the use of the telescope. 

 An opinion has indeed been current that 

 they may be discerned by a strong un 

 assisted eye, but it appears to be er 

 roneous. Sir John Herschel remarks 

 that Dr. Wollaston, who had a keen eye, 

 never succeeded in so observing them, 

 though he cut off the light of the planet 

 by hiding the body behind a distant ob 

 ject. The satellites are named after their 

 respective position in relation to the primary, the nearest to him being the first. Their 

 comparative distances and magnitudes may be thus expressed: 



Fi'rsi 



o 



Third 



Jburtl 

 -9 



The largest of these bodies is thus the third in point of distance ; the next in magnitude 

 is the fourth ; the third in magnitude is the first ; and the smallest is the second, being 

 rather less than our own moon. It is in striking accordance with the case of our 

 satellite, that the moons of Jupiter always turn the same face towards him, and thus 

 make one rotation upon their axes while accomplishing one orbital revolution. These 

 attendants are obviously designed to give him a splendid night in compensation for a 

 day less lustrous than that which we enjoy ; and it deserves notice that their orbital 

 motions are so arranged that they can never be all new moons, and consequently invisible, 

 at the same time. The position of the satellites with respect to each other, and to their 

 primary, as seen from the earth, is very variable. Sometimes they appear ranged in a 

 line on each side of the planet ; at other times they are all grouped on the same side ; 

 and on Nov. 2, 1681, Jupiter appeared deserted by his guards, three being on his disk, and 

 one behind his body. This rare phenomenon was also noticed September 27, 1843. 



