CONCLUSION. 



In concluding the uranological part of the physical de» 

 fcription of the universe, in taking a retrospect of what 1 

 have attempted (I do not say accomplished), after the exe- 

 cution of so difficult an undertaking, I think it necessary once 

 more to call to mind that this execution could have been ef 

 fected only under those conditions which have been indicated 

 in the Introduction to the third volume of Cosmos. The 

 attempt to carry out such a cosmical treatment of the subject 

 is limited to the representation of space and its material con- 

 tents, whether aggregated into spheres or not. The character 

 of the present work differs, therefore, essentially from the more 

 comprehensive and excellent elementary ivories on astronomy 

 which the various literatures of modern times possess. As- 

 tronomy, as a scieiice, the triumph of mathematical reason- 

 ing, based upon the sure foundation of the doctrine of gravi- 

 tation and the perfection of the higher analysis (a mental in- 

 strument of investigation), treats of phenomena of motion 

 measured according to space and time ; locality (position) of 

 the cosmical bodies in their mutual and perpetually-varying 

 relations to each other ; change of form, as in the tailed 

 comets ; change of light, as the sudden appearance or total 

 extinction of the light of distant suns. The quantity of mat- 

 ter present in the universe remains always the same ; but 

 from what has already been discovered in the telluric sphere 

 of physical laws of nature, we see working in the eternal 

 round of material phenomena an ever-unsatisfied change, 

 presenting itself in numberless and nameless comhhiations. 

 Such an exercise of force by matter is called forth by its at 

 least apparent heterogeneity. Exciting motion in immeas- 

 urably minute spaces, this heterogeneity of matter compli- 

 cates all the problems of teri'estrial phenomena. 



The astronomical problems are of a simpler nature. 

 Hitherto unencumbered by the above-mentioned complica- 

 tions, directed to the consideration of the quantities of pon- 

 derable matter {masses), to the osc^7Za^^o?^s ' producing light 

 and heat — the mechanics of the heavens has, precisely on 

 account of this simplicity, in which every thing is reduced to 



