208 SEE— RESULTS OF RECENT [April 23. 



of our system is to be estimated only in billions of years. This 

 prolongation of the period allowed for the activity of the sun is 

 confirmed by other investigations made by the writer during the 

 past two years, showing that the mode of formation of our system 

 has been excessively slow and very different from what has been 

 generally supposed ; and that the principal agency which has oper- 

 ated in its development and in shaping the orbits has been the 

 action of a resisting medium extending over immense periods 

 of time. 



I shall not attempt to treat fully of this large subject in the 

 present communication, because it is to be discussed in considerable 

 detail in the second volume of my " Researches on the Evolution of 

 the Stellar Systems," which is now in press and expected to appear 

 during the coming summer or autumn. But it may be useful to 

 give a brief review of the subject to see where we stand, and to sum 

 up what appears to be established by the investigations which have 

 so fully absorbed my energies during the past two years. The 

 present discussion must therefore consist mainly of a summary, 

 and such explanations as will render it moderately intelligible to 

 the general reader. 



In the first place, it is desirable to remark that, for nearly a 

 century, we followed Laplace's assumptions in regarding the planets 

 as having been detached or thrown off from the sun, and the satel- 

 lites as having been likewise thrown off from their several planets ; 

 and our problem was to find out how the postulated rings of vapor 

 had condensed into the bodies now observed in the solar system. 

 Thus with a fixed premise we were trying to find out how the 

 planetary development had come about, and it scarcely occurred to 

 any one that the premise itself might be false, and therefore all 

 the efforts based on it in vain. 



The turning point which enabled me to discover this error in 

 the premises was a certain criterion based on the law of areas pro- 

 posed by the distinguished French physicist Babinet, in 1861.^ In 

 this brief communication of three pages to the Paris Academy of 

 Sciences, Babinet pointed out the contradiction of Laplace's cos- 



^ Cf. Coniptcs Rendus, March 18, 1861. 



