130 Prof. P. E. Chase on Radiation and Rotation. 



It seems probable that, in consequence of subsidence, Ju- 

 piter, which 3 as we have already seen, was the centre of nucleal 

 volume, may have also been the centre of nucleal mass at the 

 time of its complete orbital separation, and that it was there- 

 fore the primitive Sun of the extra-asteroidal planets before it 

 became our Sun's " companion star." For with the present 

 mass of the system, and with a mean radius vector = -1^1+ ill 

 (34*4845), the orbital period of Neptune would be 73,966 days. 

 Two successive subsidences (34*4845 -r-w 2 ) would bring the 

 solar nucleal surface to about § of $ 3 , or 54*53 solar radii. 

 The angular acceleration of rotation, due to subsequent nucleal 



contraction, would oc -v,. Therefore, when the Sun had con- 



traeted to its present limits, its rotation-period would be 

 73966-*-54*53 2 = 24*88 days*. 



If this were the only coincidence of its kind, we might per- 

 haps have some good grounds for looking upon it as merely 

 curious and accidental ; but the bond of connexion which we 

 have already found between rotation and revolution, in the 

 limiting formative undulations which are propagated with the 

 velocity of light, may prepare us for accepting evidences of a 

 similar bond in the phenomena of nebular subsidence. 



There are three other known systems of cosmical rotation 

 which may help us to judge as to the rightfulness of such an 

 acceptance, viz. : — that of the extra-asteroidal planets, with an 

 estimated average period of about 10 hours ; that of the intra- 

 asteroidal planets, with an estimated period of about 24 hours; 

 and that of the moon, with a synodic period of 29*5306 days. 

 If these periods are dependent upon the same subsidence which 

 led to the early belt-formations, we may reasonably look for 

 evidence of that dependence of a character similar to that 

 which we have found in the case of the sun. 



We have seen that the first subsidences from 2 y and 3 ii 

 account for the orbital ruptures of Jupiter and Earth ; second- 

 ary subsidences from points within the orbital belts account 



* These relations may have an important bearing on Croll's hypothesis 

 of the origin of solar radiation. In the stellar-solar paraboloid, of which 

 traces still exist between Sun and a. Centauri, there must have been fre- 

 quent collisions. Some of Croll's critics have shown strange misappre- 

 hensions as to the possible velocity of collision. The limit of possible 

 relative velocity, from the simple gravitation of two equal meeting masses, 

 is 2s/2gr. This would be equivalent, taking the values of g and r at Sun's 

 apparent surface, to '01774 r, or more than 750 miles per second. If pro- 

 jection were added to gravitation, or if the two masses had small solid 

 nuclei of great density, while the greater part of their volume was gaseous, 

 or if there were a large number of equal masses, the limit of possible velo- 

 city might be largely increased, 



