THE PLANETS, AKE THEY INHABITED \ 



terrestrial in the ratio of 1 to 2*42, it follows that in a Jovian year 

 there are 10485 Jovian days. 



The Saturnian year is equal to 29| terrestrial years, or more 

 exactly to 10,759 terrestrial days, and since the Saturnian day is 

 shorter than the terrestrial in the ratio of 1 to 2'3, it will follow 

 that the Saturnian year consists of 24746 Saturnian days. 



Thus each of the Saturnian seasons, spring, summer, autumn, 

 and winter is equal to seven-and-a-half terrestrial years. 



The TJranian year is equal to 84 terrestrial years, or 30687 

 terrestrial days ; and the TJranian day, according to the probable 

 estimate, being shorter than the terrestrial day in the ratio of 

 1 to 2^, it follows that the Uranian year consists of 77336 

 Uranian days. 



If the axis of Uranus be inclined to the plane of its orbit like 

 that of Saturn, its seasons will be similar to those of the earth, 

 but of very different duration, their length being 21 terrestrial 

 years, or 19334 Uranian days. 



9. One of the most remarkable meteorological consequences 

 of the diurnal rotation of the earth is the system of atmospheric 

 currents, which, in both hemispheres, are directed generally 

 parallel to the equator, and which, from their great permanence 

 and regularity in the lower latitudes, have, in all ages since the 

 invention of ocean navigation, subserved the purposes of com- 

 merce so extensively as to have acquired the name of the trade- 

 winds. These phenomena will be explained more fully, so far as 

 relates to their physical causes, in another part of this 

 series. What we now desire to direct attention to is their 

 effects in the upper strata of the atmosphere. 



It is evident that such currents must have a general tendency 

 to distribute the strata of clouds in lines or streaks, more or less 

 pronounced, according to their intensity and regularity, parallel 

 to the equator. If these aerial currents were much more intense 

 and much more permanent and regular, and if the clouds them- 

 selves were more voluminous and permanent than they are, this 

 distribution of them in streaks or layers at right angles to the 

 earth's axis would be in proportion more pronounced, more 

 regular, and more permanent. 



The causes of these atmospheric currents are traced to the 

 combined effects of the velocity with which the atmosphere is 

 carried round with the earth on its axis, and the influence of the 

 solar heat produced upon the zone of atmosphere over those 

 regions of the globe which extend to a certain distance north and 

 south of the equator. 



If the velocity with which the atmosphere is carried round 

 were much greater than it is, and if the atmosphere were more 

 36 



