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H. Hdmholtx on the Interaction of Natural Forces. 203 



from the physical processes of terrestrial bodies as 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 es- 

 sentially 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 are composed of exactly the same simple 

 chemical substances as those with 'which we are acquainted. 

 "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 of force capable of action which it 



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A number of singular peculiarities in the structure of our 

 planetary system, indicate that it was once a connected mass 

 ^ith a 'uniform motion of rotation. Without such an assump- 

 tion 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 mucli besides. From 

 these remaining indications of a former state, astronomers have 

 hapcd an hypothesis regarding the formation 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, and the 

 3nore so, as this notion first found utterance in our own home 

 and within the walls of this town.* It was Kant who, feeling 

 great interest in the physical description of the earth and the 

 planetary system, undertook the labor of studying the w^orks 

 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 af )re- 

 time 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 Meranfgne Celeste, laid 

 told of the same thought, and introduced it among astnmomci^. 

 The commencement of our planetary system, including the 

 sun, must, according to this, be regarded as an immense nebu* 



,ed 



# Konigsberg, 



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