TRANSLATOR'S INTRODUCTION Ixxix 



Nebula the internal actions are held to be suffi- 

 cient to produce a regular movement of rotation 

 of the whole. . . . This Nebula is formed of a 

 central condensation around which particles inde- 

 pendent of each other, forming a sort of dust 

 matter, circulate in isolated orbits according to 

 Kepler's laws. The Nebula of Laplace is a true 

 atmosphere, formed of an elastic gas, whose entire 

 mass turns with the same angular velocity as the 

 central condensation, in virtue of an original move- 

 ment whose cause not indicated is beyond the 

 Nebula itself.' * This Nebula differs essentially 

 from that which Kant has placed at the basis of 

 his system. Kant's Nebula is formed of inde- 

 pendent particles which, originally, in a state of 

 repose, begin to circulate around the centre, each 

 with its own velocity, determined by the law of 

 areas. Laplace's Nebula is an atmosphere, formed 

 of an elastic gas, all the layers of which are 

 animated by the same angular velocity of rotation, 

 and which is subject to all the laws laid down by 

 Laplace in his study of atmospheres ; it has a limit 

 which is the point where the centrifugal force, due 

 to its motion of rotation, balances the gravity; it 

 has the form of an ellipsoid, whose oblateness 

 cannot exceed one-third.' Les Hypotheses Cosmo- 

 goniques, Ch. II. The two theories are thus con- 

 trasted by A. J. von Oettingen, who brings out a 

 profound difference between them : * Kant starts 

 from the primitive Nebula in the Universe ; La- 



