ICO ANNUAL OF SCIENTIFIC DISCOVERY. 



applicable also to the heavenly bodies, let me remind you that the same 

 force which, acting at the earth's surface, we call gravity, (Schwere) acts as 

 gravitation in the celestial spaces, and also manifests its power in the motion of 

 the immeasurably distant double stars which are governed by exactly the same 

 laws as those subsisting between the earth and moon ; that, therefore, the 

 light and heat of terrestrial bodies do not in any way differ essentially from 

 those of the sun, or of the most distant fixed star ; that the meteoric stones 

 which sometimes fall from external space upon the earth arc composed of 

 exactly the same simple chemical substances as those with which we are ac- 

 quainted. "We need, therefore, feel no scruple in granting- that general laws 

 to which all terrestrial natural processes are subject, are also valid for other 

 bodies than the earth. "We will, therefore, make use of our law to glance 

 over the household of the universe with respect to the store offeree, capable 

 of action, Avhich it possesses. 



A number of singular peculiarities in the structure of our planetary sys- 

 tem indicate that it was once a connected mass with a uniform motion of 

 rotation. Without such an assumption it is impossible to explain why all 

 the planets move in the same direction round the sun, why they all rotate in 

 the same direction round their axes, why the planes of their orbits, and those 

 of their satellites and rings all nearly coincide, why all their orbits differ but 

 little from circles, and much besides. From these remaining indications of 

 a former state, astronomers have shaped an hypothesis regarding the forma- 

 tion of our planetary system, which, although from the nature of the case it 

 must ever remain an hypothesis, still in its special traits is so well supported 

 by analogy, that it certainly deserves our attention. It was Kant, who, feel- 

 ing great interest in the physical description of the earth and the planetary 

 system, undertook the labor of studying the works of Newton, and as an 

 evidence of the depth to which he had penetrated into the fundamental ideas 

 of Newton, seized the notion that the same attractive force of all ponderable 

 matter which now supports the motion of the planets, must also aforetime 

 have been able to form from matter loosely scattered in space the planetary 

 system. Afterwards, and independent of Kant, Laplace, the great author 

 of the Mecanique Celeste, laid hold of the same thought, and introduced it 



among astronomers. 



The commencement of our planetary system, including the sun, must, ac- 

 cording to this, be regarded as an immense nebulous mass which filled the 

 portion of space which is now occupied by our system, far beyond the limits 

 of Neptune, our most distant planet. Even now we perhaps see similar 

 masses in the distant regions of the firmament, as patches of nebula;, and 

 nebulous stars ; within our system also, comets, the zodiacal light, the 

 corona of the sun during a total eclipse, exhibit remnants of a nebulous 

 substance, which is so thin that the light of the stars passes through it uu- 

 enfcebled and unrefracted. If we calculate the density of the mass of our 

 planetary system, according to the above assumption, for the time when it 

 was a nebulous sphere, which reached to the path of the outmost planet, we 

 should find that it would require several cubic miles of such matter to weigh 

 a single grain. 



