112 Esmark mi the Geological History of the Earth. 



globe ? With regard first to the change in the form of its orbit, 

 this must be a matter of very difficult proof; to accomplish such 

 a change, requires a period of incalculable length, and if it has 

 taken place to such a degree, we ought to find the change still 

 going on, approaching nearer and nearer to a circular orbit. 

 By the period of the earth's annual revolution round the sun, 

 we cannot ascertain this point ; for though this continues SQ5\ 

 days without change, every day, every hour, every second, may 

 be shorter, without our being able to discover this. La Place 

 computes, that, since the time of Hipparchus, who lived about 

 900 years ago, the year has become some few seconds shorter. 

 However inconsiderable this quantity may be, it proves a real 

 change. Probably the change was greater at first, diminishing 

 as the orbit of the earth approaches a circular form. Does the 

 present physical constitution of the earth, and the phenomena 

 which occur on it, countenance the idea of the orbit of the earth 

 having at first been a long ellipse ? From our present knowledge 

 of chemistry and mineralogy, we cannot adopt the idea of Whis- 

 ton, that, in its perihelium, the earth underwent a process of vi- 

 trification, in the sense in which we now understand the word. 

 The solid body of our globe consists of various minerals, com- 

 posed of different kinds of earth, combined together in certain 

 proportions. In former times, these were considered as simple 

 bodies, or, as they were called, elements. But by the discoveries 

 of the illustrious chemists Davy and Berzelius, it has been 

 found, that not only potass and natron, but that all kinds of 

 earths, which we formerly considered as simple, are compound 

 bodies, each species consisting of a peculiar base, with a fixed 

 proportion of oxygen. 



The form of the earth, a spheroid compressed at the poles, 

 proves, 1^^, That, at its original formation, it was in a state of 

 perfect fluidity. SJ, That to account for this figure, it must 

 have revolved on its axis with more velocity than it does now, 

 as it is higher at the equator, and more compressed at the poles, 

 than it ought to be from the laws of gravity with its present ve- 

 locity. From its original fluidity, all sorts of mineral bodies 

 must have been dissolved in a fluid medium. When we assume 

 that a body undergoes combustion in being combined with oxy- 

 gen, by which it is by no means to be considered as destroyed 



