TRADE WINDS AND BELTS. 



constantly and heavily loaded with clouds, these effects would be 

 much more striking. 



The velocity with which the atmosphere is carried round 

 would be greater if the earth's rotation were more rapid. It 

 would also be greater, even with the present rate of rotation, if 

 the earth were a larger globe, because then the atmosphere 

 would be carried in the same time round a proportionately 

 greater circumference. But if both these conditions were at the 

 same time fulfilled if the earth revolved more rapidly on its 

 axis, and were at the same time a larger globe, the atmosphere 

 would be not only carried round in a less time, but would revolve 

 through a larger circumference. 



10. NoW this is exactly the case with the major planets. Jupiter, 

 Saturn, and Uranus make each about five revolutions on their 

 axes while the earth makes two, and the equatorial circum- 

 ference of Jupiter is eleven times, that of Saturn above nine 

 times, and that of Uranus more than four times greater than the 

 equatorial circumference of the earth. 



The speed with which the equatorial zone of air is whirled 

 round on Jupiter is therefore about 27 times, on Saturn 23 

 times, and on Uranus about 7 times greater than on the earth. 



We find by telescopic observation also, as has been already 

 stated, that the atmospheres of these planets are so thickly and 

 constantly, loaded with clouds that the surfaces of the solid 

 globes are permanently concealed from us. 



It may, therefore, be inferred that the prevalence of atmo- 

 spheric currents on these planets parallel to their equators are 

 far more constant and more strong than upon the earth ; and 

 since the masses of cloud with which they are loaded are greater 

 and more permanent, the effects of such currents upon their 

 distribution in equatorial strata or bands must be supposed to 

 be far more conspicuous. 



11. Observation has confirmed this in a most remarkable and 

 interesting manner. Look at the six telescopic views of Jupiter, 

 given in figures 1 to 6 (page 38), which are engraved after the 

 telescopic drawings of Herschel and Madler. 



The streaks parallel to the Jovian equator are conspicuous. 

 These streaks, which were seen not long after the invention of 

 the telescope, are called " Jupiter's Belts." 



Of all the bodies of the system, the moon perhaps alone 

 excepted, Jupiter presents to the telescopic observer the most 

 magnificent spectacle. Notwithstanding its vast distance, such 

 is its stupendous magnitude that it is seen under a visual angle 

 nearly twice that of Mars. A telescope of a given power, there- 

 fore, shows it with an apparent disc four times greater. It has 



37 



