A HISTORY OF SCIENCE 



when all the suns of a system will be drawn together 

 and destroyed by impact at a common centre. Al- 

 ready, it seems to Herschel, the thickest clusters have 

 "outlived their usefulness" and are verging towards 

 their doom. 



But again, other nebulae present an appearance sug- 

 gestive of an opposite condition. They are not re- 

 solvable into stars, but present an almost uniform ap- 

 pearance throughout, and are hence believed to be 

 composed of a shining fluid, which in some instances is 

 seen to be condensed at the centre into a glowing mass. 

 In such a nebula Herschel thinks he sees a sun in 

 process of formation. 



THE NEBULAR HYPOTHESIS OF KANT 



Taken together, these two conceptions outline a ma- 

 jestic cycle of world formation and world destruction 

 a broad scheme of cosmogony, such as had been vague- 

 ly adumbrated two centuries before by Kepler and in 

 more recent times by Wright and Swedenborg. This 

 so-called "nebular hypothesis" assumes that in the 

 beginning all space was uniformly filled with cosmic 

 matter in a state of nebular or "fire-mist" diffusion, 

 "formless and void." It pictures the condensation 

 coagulation, if you will of portions of this mass to 

 form segregated masses, and the ultimate development 

 out of these masses of the sidereal bodies that we see. 



Perhaps the first elaborate exposition of this idea 

 was that given by the great German philosopher Im- 

 manuel Kant (born at Konigsberg in 1724, died in 

 1804), known to every one as the author of the Critique 

 of Pure Reason. Let us learn from his own words how 



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