THE MAJOR PLANETS. 



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239 ! 



The great length of Jupiter's year compared with its rapid diurnal rotation, 

 will resolve the year into a much greater number of days than its proportional 

 length compared with the terrestrial year would infer. While Jupiter makes 

 one complete revolution round the sun, it will make ten thousand four hundred 

 and seventy revolutions on its axis. Such, therefore, is the number of days 

 in Jupiter's year. 



The axis of Jupiter is inclined to its orbit at an angle of about three degrees, 

 and as this inclination determines the limits of the seasons, it follows that there 

 can be scarcely any perceptible change of season upon the planet during one 

 half of his year. The sun will, during one half year, gradually pass to three 

 degrees north of his equator, and during the other half year to three degrees 

 south of it. The extreme change of the sun's meridional altitude would there- 

 fore not exceed six degrees. This perhaps might be sufficient for the purposes 

 of chronology, but could scarcely produce any effects on the organized world, 

 nor would the temperature of the seasons undergo any observable change. The 

 range of the tropics would be three degrees on each side of the equator of the 

 planet, and within these regions the sun would pass near the zenith daily. 



The sun would rise and set daily throughout the year, to every part of the 

 planet except a small circle extending three degrees round the poles. 



The diameter of Jupiter being eleven times that of the earth, his surface will 

 be greater than that of our planet in the proportion of a hundred and twenty to 

 one, and if the distribution of land and water be similar, it will afford accom- 

 modation for a population a hundred and twenty times more numerous. 



The actual bulk of the globe of Jupiter, which is the largest body of the 

 system next to the sun, is fourteen hundred times greater than that of the earth. 

 In other words, to make a globe equal to that of Jupiter, we should roll into 

 one fourteen hundred globes like that of the earth. 



TELESCOPIC APPEARANCE OF JUPITER. 



The spectacle presented to the observer who enjoys the use of a powerful 

 telescope by the planet Jupiter, is magnificent indeed. The surface of the 

 planet appears as large and distinct as the full moon to the naked eye. His 

 disk is marked with certain features of light and shadow, which are in general 

 variable. They are, therefore, produced by clouds floating in his atmosphere, 

 the presence of which is indeed rendered quite evident by the telescope. Al- 

 though these lights and shadows in general are variable, yet they are found 

 to be characterized by a certain regularity of arrangement. Their streaks 

 are generally parallel, as in the annexed figures, which exhibit views of Jupiter 

 seen on different occasions. 



These streaks, which are called the belts of Jupiter, were observed before 

 the middle of the 17th century, and are visible to telescopes of no very con- 

 siderable power. They are variable not only in their breadth and form, btit 

 in their number. Sometimes not more than one can be discovered ; at other 

 times two or more, and sometimes as many as eight. Sometimes they have 

 continued without sensible variation for nearly three months, and sometimes a 

 new belt has appeared in an hour or two. The annexed diagrams have been 

 given by different authors as representing the appearances of these belts at 

 different times. They have, sometimes, though rarely, been see-n broken ujp 

 and distributed over the whole surface of the planet as represented in fig. D. 

 Fig. B gives a view taken at an early period by Dr. Hook. Fig. A is a view 

 taken in the year 1832. Fig. C is in 1837. It is, however, extremely dif- 

 ficult to obtain sketches of this kind executed with tolerable fidelity. 



Mr. Thomas Dick states that he has had frequently an opportunity of view- 



