182 IN STARRY REALMS. 



pensates for his distance in so far as the size and general 

 effectiveness of his telescopic picture is concerned. 



A view showing the relative dimensions of the chief 

 planets in our system compared with the sun is given in 

 Fig. 17. 



Jupiter is obviously flattened at the poles and pro- 

 tuberant at the equator. Our earth is also shaped in 

 a similar fashion, but the extent of the protuberance on 

 the earth is much less than that on Jupiter. Nor is 

 it difficult to explain the reason of this peculiarity of 

 shape, and of the excessive degree in which Jupiter is 

 affected by it. We have already seen that Mars revolves 

 on its axis, as does our earth, and we might probably 

 assert that rotation of this kind was a universal attribute 

 of celestial bodies at all events, Jupiter possesses it in a 

 very marked degree. Though our little globe for little 

 it must be regarded beside Jupiter takes 24 hours to go 

 round, yet Jupiter accomplishes his complete spin in less 

 than half as much in fact, in 9 hrs. 55 mins. 



Owing to the rapidity of Jupiter's rotation and to the 

 immense size of the planet, the actual speed of the surface 

 of the body must be enormously great. A point on the 

 equator of Jupiter moves about twenty- seven times as fast 

 as a point on our equator. The protuberance at the 

 equator of the great planet is to be ascribed to this fact. 

 As the body is revolving so rapidly, the yielding materials 

 of which it is made accommodate themselves to the shape 

 which nature demands, and the characteristic aspect of 

 the planet is the result. 



We have seen that Mars is a body, in some respects, at 

 all events, resembling or analogous to our earth. In fact, 



