TJDAL EVOLUTION. 13 



far not found it necessary to even mention the solar tides. 

 But when the earth-moon system has attained equilibrium the 

 sun-raised tides will continue right on in their action. To be 

 sure, they are very small compared to those raised by the 

 moon, but it is well to remember that it is just these small 

 forces acting day in and day out, silently, quietly, persistently, 

 uninterruptedly in the same direction, which in the end 

 accomplish stupendous results. When the earth and moon 

 shall have come to a mutual rest, the solar tides will continue 

 to retard the earth in her diurnal motion until at last the day 

 will become longer than the month. 



This may seem to many to be an impossible state of af- 

 fairs that the month which is now 27 times longer than the 

 day should actually become shorter. But why not? If these 

 conditions existed today they would be just as natural to us as 

 our present. In fact, we are able with a great deal of satis- 

 faction to corroborate our reasoning with a remarkable example 

 in our solar system. The planet Mars is but little more than 

 half the size of our earth. We are therefore justified in 

 believing that this brother sphere has passed through his 

 evolution quicker and is further along the road of his destiny 

 than is the case with our earth. With this in mind it is 

 interesting to find that in the case of this planet and his satel- 

 lite Phobes, the Martian day is actually three times longer 

 than the periodic time of the satellite a signal prophesy ot 

 the future of our own earth-moon system. 



For the same reason that we expected Mars to be in 

 advance of our earth in his evolution, we would anticipate 

 Jupiter on the other hand to befar behind. On this giant planet, 

 which is so much larger and so much farther distant from our sun 

 its center of heat and attraction, we may confidently expect 

 to find conditions prevailing which existed on our earth many 

 millions of years ago. And, indeed, in this we shall not 

 find ourselves to have judged wrong. It does not take very 

 many observations with a powerful telescope to tell that this 

 planet is not solid, but is rather in a plastic, if not even in,, a 

 molten condition. But most significant of all, his axial revo- 

 lution is accomplished in about 10 hours a phenomenon which 



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