462 THE POPULAR SCIENCE MONTHLY. 



Swedenborg postulates a solar vortex, from which is gradually detached 

 a ring, by the disruption of which the planetary globes and their satel- 

 lites are formed.* Twenty years later analogous ideas were held by Im- 

 manuel Kant, who, it would seem, merely commented on and developed 

 the views of Thomas Wright. f In this system the planets are formed 

 directly by the condensation of nebulous matter without the inter- 

 mediate formation of rings. These theories are curious in the light 

 of the history of science. There is also the theory of Buffon, who 

 imagined that a comet, striking the sun, forced from it a stream of 

 matter that agglomerated to form the planets. But Laplace was the 

 first to offer a theory of the origin of the solar system that was founded 

 on rigorously scientific principles, and that conformed to the data of 

 celestial mechanics. That which distinguishes the conceptions of his 

 genius is, that the discoveries since made, far from weakening his 

 hypothesis, seem on the contrary to daily strengthen it. 



Laplace conceived all the stars formed by the gradual concentration 

 of a nebulosity diffused in space, which became luminous in pi-oportion 

 as it condensed, under the force of gravitation. The sun itself was at 

 first nebulous, with a brilliant nucleus. Supposing the system endowed 

 with a rotary movement and this is an unavoidable postulate the 

 solar atmosphere at first assumed a figure of spheroidal equilibrium, 

 much flattened, and limited in its dimensions by the zone where the 

 centrifugal force counterbalanced the weight. The molecules situated 

 beyond this limit ceased to belong to the atmosphere proper, and re- 

 volved freely around the central star as planetary masses. Now, a law 

 of mechanics teaches that in proportion as the cooling contracts the 

 atmosphere and condenses the molecules in the vicinity of the nucleus, 

 the rotation becomes more rapid ; the centrifugal force thereby aug- 

 menting, the point where the weight counterbalances it is brought 

 nearer the center, and the particles banished to the outskirts become 

 planets. Contracting little by little, the solar atmosphere became sep- 

 arated from the zone of vapors in the plane of its equator. These 

 abandoned vapors, wrecks of the solar ocean, must first have formed 

 concentric rings circulating around the sun, comparable to the rings of 

 Saturn. These rings would soon break up into several masses, which, 

 speedily conglobulating, assumed , a rotary movement in the direction 

 of their revolution around the sun. It is thus that the planets origi- 

 nate, and give birth, in cooling, to the satellites that accompany them. 

 " Hence," says Laplace, " the notable phenomenon of the slight eccen- 

 tricity of the orbits of the planets and their satellites ; of the slight 

 inclination of these orbits to the plane of the solar equator ; and of the 

 identity of movement, in rotation and revolution, of all these bodies 

 with that of the sun, giving to the hypothesis we offer a high degree 



* The chapter is entitled " De chao universali solis et planetarum, deque separatione 

 ejus in planetas et satellites." 



f "An Original Theory or New Hypothesis of the Universe." London, 1750. 



