Dr. J. Croll on the Origin of Nebulae. 11 



yet received their store of light and heat, while there are 

 others which have entirely * lost it. The stars are probably 

 only those stellar masses which having recently had an en- 

 counter have become possessed of light and heat. They have 

 gained in light and heat what they have lost in motion, but 

 they have gained a possession which they cannot retain, and 

 when it is lost they become again what they originally were 

 — dark bodies. 



2nd. " We have no instances of stellar motions comparable 

 with those demanded by the theory."" A little consideration 

 will show that this is an objection which, like the former, can 

 hardly be admitted. No body of course moving at the rate 

 of 400 miles per second could remain a member of our solar 

 system ; and beyond our system the only bodies visible are the 

 nebulse and fixed stars ; and they are according to the theory 

 visible because like the sun they have lost their motion — the 

 lost motion being the origin of their light and heat. Their 

 comparatively small velocities are in reality evidence in favour 

 of the theory than otherwise ; for had the stars been moving 

 with excessive velocities this would have been adduced as 

 proof that their light and heat could not have been derived 

 from motion lost, as the theory assumes. 



3rd. " If suns or stars have been formed by collision of bodies 

 moving in space, proper motion can be none other than the 

 unused and unconverted energy of the original components. 

 And as stellar bodies are likely of all sizes and moving with 

 all manner of velocities, it must often happen, from the unequal 

 force of the impinging masses, that a large proportion of the 

 original motion must remain unconverted into heat. Conse- 

 quently some of the stars ought, according to the theory, to 

 possess great velocities — which is not the case, as none of the 

 stars have a motion of more than 30 or 40 miles per second." 

 I freely admit that, if it could be proved that none of the 

 stars have a proper motion of more than 30 or 40 miles per 

 second, it would at least be a formidable difficulty in the way 

 of accepting the theory. For it would indeed be strange that 

 amidst all the diversity of dimensions of heavenly bodies, it 

 should invariably happen that the resultant movement of the 

 combined masses should be reduced to such comparatively in- 

 significant figures. But something more definite must yet 

 be known in reference to the motion of the stars before this 

 objection can be urged. 



All that we are at present warranted to assume is simply 

 that, of the comparatively few stars whose rate of motion has 

 been properly measured, none have a greater velocity than 30 

 or 40 miles per second, while nothing whatever is known 



