578 THE POPULAR SCIENCE MONTHLY.. 



There is, indeed, no doubt that, under such circumstances, the flattening 

 would be about four times as great as it is now, so that the difference 

 between the equatorial and polar diameters would be about a hundred 

 miles ; and then the age of our world might be found as accurately as 

 its distance from the sun. Now, the neighboring zone of the solar sys- 

 tem presents an actual case very similar to the extreme one under con- 

 sideration. The difference between the equatorial and polar diameters 

 of Mars is at least three times as great as that which could be expected 

 from his present rotation if he were in a fluid condition. On taking 

 even the lowest values which observers give for his compression, it 

 must be concluded that, since changing his primitive fluid state and 

 becoming solid and inflexible, the planet must have lost about forty per 

 cent, of its diurnal motion. It evidently follows, according to Prof. 

 Tait's rule, that about 800,000,000 years elapsed since the solidification 

 took place, supposing the length of the day of Mars increased at the 

 same rate as that of our globe. But the same great number will seem 

 scarcely adequate to express the centuries since the event, when we 

 consider that the rotation of our planetary neighbor is checked, not by 

 strong tidal friction, but by the more feeble impediment from the re- 

 sisting medium of space. 



In two publications, during 1856 and 1858, I discussed the geologi- 

 cal consequences of the slow reduction in the earth's diurnal motion ; 

 and many reasons led me to the conclusion that the long-continued 

 decline of centrifugal force would make our planet undergo a change 

 of form, by the gradual retirement of water to the poles, and, after long 

 ages, by the upheaval of the bottoms of the polar oceans. I also main- 

 tained that such upheavals of circumpolar lands would be prevented by 

 the strength of the crust of a small planet, and that Mars would be able 

 to preserve for an exceedingly long period the form impressed on him 

 in the very early term of his existence. The earth's internal fluidity, 

 which I regarded as playing a very important part in such rare par- 

 oxysmal events, has been long a favorite doctrine with geologists, and 

 has been often invoked as a means of accounting for the oft-repeated 

 cases of elevation and submergence in the ancient world. But, on a 

 globe entirely solid and inflexible, there would seem to be no scope or 

 even possibility of the vast changes recorded in geological history ; and 

 speculative astronomy, in curtailing the time and restricting the means 

 of great physical revolutions, makes the information from organic re- 

 mains difficult to be understood and deficient in value. Since the au- 

 thority of Hopkins gave currency to the doctrine of the internal solid- 

 ity of our globe, much scientific talent has been expended in attempt- 

 ing to account for the great geological changes ; but the causes which 

 have been appealed to would require millions of centuries to produce 

 the results ascribed to them. It seems very difficult to set aside the 

 opinion which has been formed of the high antiquity of the physical 

 world, not only from the marks in the terrestrial crust of repeated ele- 



