PIERRE SIMON LAPLACE 141 



two nuclei, will in like manner form stars very near to each other, 

 revolving the one about the other like to the double stars, whose 

 respective motions have been already recognized. 



But in what manner has the solar atmosphere determined the mo- 

 tions of rotation and revolution of the planets and satellites? If 

 these bodies had penetrated deeply into this atmosphere, its resistance 

 would cause them to fall on the Sun. We may therefore suppose that 

 the planets were formed at its successive limits, by the condensation 

 of zones of vapours, which it must, while it was cooling, have 

 abandoned in the plane of its equator. 



Let us resume the results which we have given in the tenth chapter 

 of the preceding book. The Sun's atmosphere cannot extend in- 

 definitely; its limit is the point where the centrifugal force arising 

 from the motion of rotation balances the gravity; but according as 

 the cooling contracts the atmosphere, and condenses the molecules 

 which are near to it, on the surface of the star, the motion of rotation 

 increases ; for, in virtue of the principle of areas, the sum of the areas 

 described by the radius vector of each particle of the Sun and its 

 atmosphere, and projected on the plane of its equator, is always the 

 same. Consequently the rotation ought to be quicker, when these 

 particles approach to the centre of the Sun. The centrifugal force 

 arising from this m.otion becoming thus greater ; the point where the 

 gravity is equal to it, is nearer to the centre of the Sun. Supposing, 

 therefore, what is natural to admit, that the atmosphere extended at 

 any epoch as far as this limit, it ought, according as it cooled, to 

 abandon the molecules, which are situated at this limit, and at the 

 successive limits produced by the increased rotation of the Sun. 

 These particles, after being abandoned, have continued to circulate 

 about this star, because their centrifugal force was balanced by their 

 gravity. But as this equality does not obtain for these molecules of 

 the atmosphere which are situated on the parallels to the Sun's 

 equator, these have come nearer by their gravity to the atmosphere 

 according as it condensed, and they have not ceased to belong to it 

 inasmuch as by their motion, they have approached to the plane of 

 this equator. 



Let us now consider the zones of vapours, which have been suc- 

 cessively abandoned. These zones ought, according to all probability, 

 to form by their condensation, and by the mutual attraction of their 



