Transformation of Nebulce into Stars. 819 



The passage of each nucleus to a stellar state, with the con- 

 tinuance of a slight surrounding nebulosity ; 



Finally, the precipitation of this last mentioned nebulosity, 

 and, as the definite result, as many stars as there were dis- 

 tinct centres of attraction in the original nebulosity. 



And in what length of time can a single and the same ne- 

 bulosity undergo all this series of transformations ? Of this we 

 are absolutely ignorant. In some instances, perhaps millions 

 of years would be necessary ; in other instances, with other 

 conditions of extent, density, physical constitution, and phos- 

 phorescent matter, much shorter periods would be sufficient, 

 as the sudden appearance of the new star of 1572 seems to 

 indicate. 



The unequal rapidity of the transformations leads to one 

 important consequence. In departing from this basis, it is evi- 

 dent that the nubulae, if they were all of the same age, must, 

 iaken altogether ^ present the various forms which I have enu- 

 merated. To one region, ages w^ould scarcely bring a visible 

 accumulation of phosphorescent matter round some centres of 

 attraction ; towards another region, owing to a more precipi- 

 tate movement of concentration, we should already find groups 

 of nebulae with a nucleus ; nebulous stars would at last pre- 

 sent themselves here and there, as the last step leading to 

 stars properly so called. 



All these states of the nebulous matter indicated by theory, 

 observation had discovered beforehand. The argument is as 

 satisfactory as could be desired ; only, instead of following the 

 transformations in a single nebula step by step, their develop- 

 ment and progress have been determined by observations made 

 on them collectively. Is it not thus that the naturalist acts, 

 when he is compelled to describe, for all ages, the habit, size, 

 form, and external appearances of the trees composing the 

 forests he is rapidly crossing ? The modifications which a very 

 young tree shall undergo, he perceives distinctly and unequi- 

 vocally with a glance of the eye at an object of the same kind 

 which has already arrived at the most complete degree of 

 growth and development. 



Jlistorical details on the transformation ofNebulcc into Stars — 



