MARS ASTEROIDS JUPITER SATURN URANUS. 



9o 



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, 

 comparative distances and magnitudes may be thus expressed ; 



Their 



lirsl 



Second 



Third 



-Q 



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 Devolution. 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 one occasion, Nov. 2, 1681, Jupiter appeared deserted by his guards, three being 

 on his disk, and one behind his body. 



