191 1.] SEE— THE NEW COSMOGONY. 263 



of the planet or satellite have been correspondingly augmented by the 

 same cause. 



6. For whilst the decrease of the major axis of the orbit of a 

 satellite might result wholly from the growth of the mass of the 

 planet and satellite, yet the decrease of the eccentricity of a satellite 

 orbit can be explained only by collisions in the nebular resisting 

 medium. This cause and no other whatsoever will explain the 

 roundness of the orbits so characteristic of the solar system. 



7. Accordingly as most of the satellites sufifered collisions suffi- 

 cient to reduce and well nigh destroy the eccentricities of their 

 orbits,- it necessarily follows that all these bodies should have their 

 surfaces indented by impacts with smaller masses, just as is shown 

 by the craters on the moon. 



8. For whilst Oppolzer, Gylden and others have proved that the 

 growth of the masses by the downfall of cosmical dust would, 

 increase the central attraction and bring the bodies close together, 

 it is proved by the mathematical researches of Airy, Herschel, Leh- 

 mann-Filhes, and Stromgren, which I have carefully verified, that 

 this decrease in the major axis does not decrease the eccentricity. 

 Hence the decrease of the eccentricity is traceable to no cause what- 

 soever but the action of a nebular resisting medium, as held in my 

 " Researches." \'ol. II., p. 146. 



9. The craters on the moon can therefore be due to no cause 

 whatsoever other than the collisions which our satellite has suffered 

 from other small bodies in space, and all divisions of opinion on the 

 subject are henceforth swept away forever. For as the other satel- 

 lites have had their orbits rounded up in nearing their several planets, 

 it is necessary to suppose the same cause to have acted also on our 

 moon, even if the eccentricity of the orbit in this case has not been 

 rendered excessively small. 



10. This solution of the problem of the roundness of the orbits — - 

 the leading problem in the cosmogony of our solar system — is what 

 mathematicians call a unique solution. It reveals not only a possible, 

 but also the only possible cause of the extremely circular niove- 



" In section 548 of his " General Astronomy," edition of 1904, the late 

 Professor C. A. Young remarks that the " almost perfect circularity of the 

 satellite orbits is not yet explained." 



