SCIENCE AT THE BEGINNING OF THE CENTURY 



Continuing his observations of the innumerable nebu- 

 lae, Herschel is led presently to another curious specula- 

 tive inference. He notes that some star groups are much 

 more thickly clustered than others, and he is led to in- 

 fer that such varied clustering tells of varying ages of 

 the different nebulae. He thinks that at first all space 

 may have been evenly sprinkled with the stars, and that 

 the grouping has resulted from the action of gravita- 

 tion. Looking forward, it appears that the time must 

 come when all the suns of a system will be drawn to- 

 gether and destroyed by impact at a common centre. 

 Already, it seems to him, 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 resolva- 

 able into stars, but present an almost uniform appear- 

 ance 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. 



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 vaguely 

 adumbrated two centuries before by Kepler, and in 

 more recent times by "Wright and Kant and Sweden- 

 borg. 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 con- 

 densation coagulation, if you wil\ of portions of this 

 mass to form segregated masses, a td the ultimate devel- 



13 



