Dr. J. R. Mayer on Celestial Dynamics. 421 



before the earth attained its present magnitude, and that luxu- 

 riant vegetation may have at different times been buried under 

 the fiery debris resulting from the conflict of these masses. 



As long as the surface of our globe was in an incandescent 

 state, it must have lost heat at a very rapid rate; gradually this 

 process became slower; and although it has not yet entirely 

 ceased, the rate of cooling must have diminished to a compara- 

 tively small magnitude. 



Two phenomena are caused by the cooling of the earth, which, 

 on account of their common origin, are intimately related. The 

 decrease of temperature, and consequent contraction of the 

 Garth's crust, must have caused frequent disturbances and revo- 

 lutions on its surface, accompanied by the ejection of molten 

 masses and the formation of protuberances ; on the other hand, 

 according to the laws of mechanics, the velocity of rotation must 

 have increased with the diminution of the volume of the sphere, 

 or, in other words, the cooling of the earth must have shortened 

 the length of the day. 



As the intensity of such disturbances and the velocity of rota- 

 tion are closely connected, it is clear that the youth of our planet 

 must have been distinguished by continual violent transforma- 

 tions of its crust, and a perceptible acceleration of the velocity 

 of its axial rotation ; whilst in the present time the metamor- 

 phoses of its surface are much slower, and the acceleration of its 

 axial revolution diminished to a very small amount. 



If we imagine the tiuies when the Alps, the chain of the Andes, 

 and the Peak of Teneriffe were upheaved from the deep, and com- 

 pare with such changes the earthquakes and volcanic eruptions 

 of historic times, we perceive in these modern transformations 

 but weak images of the analogous processes of bygone ages. 



Whilst we are surrounded on every side by the monuments 

 of violent volcanic convulsions, we possess no record of the 

 velocity of the axial rotation of our planet in antediluvian times. 

 It is of the greatest importance that we should have an exact 

 knowledge of a change in this velocity, or in the length of the 

 day during historic times. The investigation of this subject 

 by the great Laplace forms a bright monument in the depart- 

 ment of exact science. 



These calculations are essentially conducted in the following 

 manner: — In the first place, the time between two eclipses 

 of the sun, widely apart from each other, is as accurately 

 as possible expressed in days, and from this the ratio of the 

 time of the earth's rotation to the mean time of the moon's 

 revolution determined. If, now, the observations of ancient 



