PLANETARY EVOLUTION 



by M. Plateau, strikingly illustrates the growth 

 of our planetary system from the solar nebula. 

 M. Plateau's experiment consists in freeing a 

 fluid mass from the action of terrestrial gravity, 

 so that its various parts may be subject only to 

 their own mutual attractions ; and then in im- 

 parting to this mass an increasingly rapid move- 

 ment of rotation. A quantity of oil is poured 

 into a glass vessel containing a mixture of water 

 and alcohol, of which the lower strata are hea- 

 vier than the oil, while the upper strata are 

 lighter. The oil, when poured in, descends un- 

 til it reaches the stratum of the same density 

 with itself, when being freed from the action of 

 terrestrial gravity, and subjected only to the 

 mutual attraction of its own molecules, it as- 

 sumes a spherical form. By an ingenious me- 

 chanical contrivance, M. Plateau now causes the 

 sphere of oil to rotate about its own centre of 

 gravity. While the movement is slow, the ex- 

 cess of centrifugal force at the equator of the 

 oil-globe causes a bulging of the equator and 

 corresponding flattening of the poles, like that 

 observed in the sun and in all the planets. 

 From a sphere the oil-globe becomes a " sphe- 

 roid of rotation." If now the movement is con- 

 siderably accelerated, the equatorial portion of 

 the oil-globe becomes detached, and surrounds 

 the central sphere of oil in the shape of a nearly 

 circular ring, like Saturn's ring-system. Finally, 

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